A couple things to remember/consider as you contemplate your engine build. The 396/402 and 427 all used the same (stroke is 3.76) crank. The bores obviously are different. In their stock configuration, all of these engines used a 6.135 rod length. There are some very good crankshaft/rod/piston kits available that use the stock dimensions. The reason I mention this is that by using stock components, you avoid machine work and know going in that the reciprocating mass will function as intended and have proper clearances. GM part numbers 3882841 (OEM in high performance 396) and 3882842 (OEM in high performance 427) are really good crankshafts. Both are forged, cross drilled, and nitride treated [improved overall strength and gives a very hard surface].

The 049 heads are pretty good. You probably have stock valves (2.06/1.72) but with a bit of machine work will accept the larger (2.19/1.88) valves that will certainly help in your quest for 450HP. I like dual springs, but there are certainly good single options and I would defer to the wisdom of others on this site for specifics here. A stock ratio (1.7) roller tip rocker arm is probably a good investment (less that $200) as well if you have the cash. Otherwise, the stockers are ok.

My number one suggestion is to keep your cam “streetable”, that is, don’t get too aggressive. A BB should produce a gob of low end and pull strong to 5000RPM plus while still behaving at idle. I always have to smile when a hear what sounds like an “eight cylinder Harley” that smells like raw gas and performs like crap and the owner can’t seem to figure out what when wrong when the cam is just too aggressive for anything less than a funny car.

Intake and carb options are numerous. I’ve always had good lock with Edelbrock manifolds and their carbs work well out of the box. Probably a Performer 2161 and a 750 cfm carb with an electric choke like the Edelbrock 1411 would give you great results.

Good luck and remember to have fun while you’re doing all this work