Welcome to CHR!

I love the 65 Impala and consider the SS to be in my top five favorite of all time. Are you set on a 350? If I were you, I'd go with a big block to move a two ton car. A lot easier to build 400 plus horsepower when starting with 454 cubic inches. A mild built big block with a 4 speed OD automatic and 3:43 posi would allow you to launch well and cruise comfortably at 70 MPH at around 2,000 RPM with a 27" tire.

A 400 horsepower small block is certainly possible and can be done in in a way that retains decent street manners. It would be easier with a 383 stroker than a stock 350 and if you're going to start from scratch, you should consider the 383 (cubic inches help to move big cars!) Bear in mind that you block will require additional machining if you opt for a 383.

Tech is spot on - get a good machinist to clean and measure the block. You will want to go with a 9.00" stack – Tech is a master here and he will certainly have a few ideas for pistons.

If you stay with iron heads, I’d opt for L31 Vortecs, casting number 12558062 or 10239906. They were used on '96-'99 Chevy trucks with the L31 5700 Vortec engine and are readily available in wrecking yards and on Craigslist / eBay (make sure they’re genuine GM heads – not knock offs!). As an aside, one of the nice things about a reputable wrecking yard is that they’ll guarantee the heads so if your machinist finds a crack you’re not out a ton money for a new one where as Craigslist and ebay purchases are typically guaranteed 30 seconds or 30 feet – whichever comes first.

These heads use rail rockers, so get the rockers with them if you can. These are some of the best flowing production heads that Chevy ever made. A good machine shop will be able to pin the studs, install new seals, and perform a 5-angle valve job. You can buy Comp Cams drop-in beehive valve springs and retainers that complement your cam and you have a great set of heads for well under a grand.

The Vortec heads are 64cc. Use a piston that gives you a static compression ratio between 9.6:1 - 9.8:1. Work with your machinist here. KB (and others) has an offset dish type piston in a D-cup configuration that provides a nice crown to complement the Vortec head configuration. Ask your machinist to cut the block decks to 9.001" for a zero piston deck height and use a 0.039" or 0.040" compressed head gasket. This should allow you to run premium pump gas without detonation. You may need some octane booster depending on the quality of your local petrol supply – in Oregon our gas is crap.

I’d go a bit smaller on the cam. A good cam would be Comp Cams part 12-262-4 or Howards CL112571-12. These are flat tappet cams so you’ll need to pay attention to break-in, but they are both proven performers that won’t break the bank and will give you great performance on the street with a lot of mid-range snap. It will have a bit of a lope but not to the extent that your friends will wonder if you have a flatulating elephant under the hood.

I like the Edelbrock Performer RPM Vortec #7116 intake manifold. This is a Vortec specific manifold that require a square bore (Holley or Edelbrock) carburetor. Stay with a 600 - 650CFM carburetor. I also really like Quadrajet carburetors so the Edelbrock 2116 with a Q-jet would be a good choice as well.

Buy some Hooker 2130-1HKR long tube, equal length headers and route through Flowmaster 40 series mufflers and route all the way out past the rear bumper. I really like ceramic coated for looks, longevity and heat dissipation. I know these are expensive, but they’ll look good for years and perform well. Nothing looks worse than rusty headers. Use good copper gaskets and locking stainless steel bolts – again expensive but leaking exhaust is not only hideous sounding it’s dangerous.

In addition to the above – make sure you get a good new oil pump with a welded or otherwise firmly affixed pickup. Miloden kit with pan, windage tray, bolts, one piece gasket, pump, and pickup is a good investment. Go with a stock 5 quart pan – resist the temptation to go with a deep pan unless you know you’ll have lots of ground clearance.

New lifters – Comp Cams (or comes as a kit with the Howard’s part number above), new timing set – double roller from Summit is fine, new HEI distributor, new water pump, and good gasket set like Felpro.

Others will jump in but this is what came off the top of my head and it should get you 400 plus horsepower and 425 ft/lbs of torque.

Couple more thoughts for you….
Have the machine shop install new cam bearings and new brass freeze plugs. Also have the machinist go over the location of all the galley plugs with you so you know where they are and that they have been properly installed. When you get the block back from the machine shop make sure you really scrub that baby down with hot soapy water. I like Dawn dish washing liquid and water straight from the bottom of the water heater. Put the block on the engine stand. If you don’t have one, buy an inexpensive Harbor Freight four wheel unit and screw a very large cookie sheet to the stand to catch dropped hardware and help keep your floor clean. Dry with compressed air really well. Make sure you have a 55 degree or warmer day and paint the inside of the engine. I use Glyptal. Its $50 a quart from Eastwood – buy the brush on and a quart will do the job real nice (I use the disposable “China” bristle brushes from Harbor Freight). Also paint the exterior at this time too. Let everything dry real well – at least 48 hours.

Stop working when you get tired and you’ll save the headache of having to redo something. I still keep a log sheet on an engine and note everything I’ve done before I quit for the day – of late I’ve started taking pictures with a digital camera then have a visual record as well. It makes it a whole lot easier to ‘take-up-where-I-left-off, especially if there are a couple days between working the engine.

Have fun and let us help!
Glenn