Hi again. My stock 428CJ runs 10.6 cr. Factory timing 6BTDC, and no problems with pinging. Stock cam (stock everything - it's just a service motor that was balanced/blueprinted before being assembled), which matches 390GT. Mild lope at 600RPM in drive. Hard on back tires, though

One of the things Morgan did when machining the heads was make sure they were smooth, and had no potential hot spots. The C8OE-N heads spec 73-76 cc chambers, while the 390GT shows 71-74 (mentioned earlier). I've run the timing up to 10BTDC without pinging here in the flats. I worried a bit about the compression, but it doesn't seem to be a problem. Wouldn't go any higher, though.

I had really good success with Morgan's Machine and Marine in Walnut Creek, CA. Tim Morgan listened, discussed what I was after, pointed out ways to save money (new heads, but I needed the numbers), and did what matched my plans. Great work and great people, IMO.

My '69 had Hooker headers on it years ago, and they ran back to collectors about halfway back on the front floor pans. Only problem was dragging on speed bumps, high/steep curbs, and a friend's gravel driveway. Oh, and you have to drop the power steering ram, but there's a bracket available to do that. Wish I had the stock one back, now. I'd trade my dropped one for the stock. Tony D. Branda, Mustangs Unlimited, and a bunch of other supply houses sell H-pipes and stock exhaust systems that hook right up to the headers. Those stock 428CJ exhaust systems should fit your 390 with headers or the CJ exh manifolds, and sound terrific. Great presence at idle, seem to flow pretty well. If you're going stock, they work well.

Only issue I've had with the stock engine (which is basically a bit larger version of the 390GT, with terrific heads and a higher rise intake) has been heating. Infrared thermometer shows 230-235 idling after a good warm-up (20 miles or so), with a 180 thermostat. Or a 160. Or a 195. Lotsa iron, new motor. Of course, new rad, too. Don't forget to look to that with your new motor.

If I weren't worried about the correct numbers/date codes, I'd run the aluminum PI manifold that's pretty readily available. It's about like the CJ intake, but probably 70 lbs lighter. Even has Ford numbers, but they aren't right for the Mustangs.

Post details as you go along. Sounds like a fun project.