Okay, here we go.........
AMX Enterprises in Arvada, CO did the rebuild. I wanted an increase in performance, milage and reliability. 1969 390, stock auto trans, 3.15 rear ratio. I rarely run over 5200 rpm, 5500 is absolute max.
It was bored .030. I went with cast pistons, stock compression of 10.2:1. Balanced it. The heads are late model 58cc off a 1973 401. Rebuilt the heads, new valve guides, springs, stainless steel valves, both sides. Hardening the seats is a waste of money, they're hard enough already. The larger 58cc chamber (stock is 51cc) equates to an approximate .6 drop in compression so it's running a 9.6:1 ratio.
Put a new timing chain cover on it - this really is a must for good oil pressure and longevity of your rebuild. At the time I bought an NOS one from Chrysler for $650.00. There were quality issues with the aftermarket pieces then. Aftermarket units are still available and I beleive they have all the initial bugs worked out. They run about $280.00 (if I remember right.)
The cam is an Erson. .478 lift / 292 duration. Highly recommend for street and weekend performance. Very slight lope. Excellent power throughout the power range but really strong from 3000-5000rpm. Very good economy.
Very sensitive to timing though.
Intake is an Edelbrock Performer. The similar (improved?) Air Gap intakes were not out at that time and I've never had one so I can't comment on those.
The carb is a Carter AFB 625 CFM (not original carb it's a later model) only 'mod' is it's jetted for this altitude (6,500 to 7,500 feet).
Distributor and coil - New but stock. Yep, good old single points.
Exhaust manifolds are stock AMC 1971 Free Flow w/o tubes. These run into 2 1/2" exhaust which go through chambered mufflers and exit via Reproduction Trendsetter sidepipes. What a sweet sound. And from 3000-5000 rpm they really open up and wow. I didn't think they were that loud until a Harley rider flipped me off.
It has the Borg Warner M12 automatic, it was rebuilt stock with a rebuilt convertor (stock stall) and an NOS flex plate.
The rear-end is original with the stock R&P. 3.15:1 Ratio.
I say "It's running 'about' 365-375 hp" because its never been dynoed. All I can do is figure the factory rated them at 315 hp and 425 ft lbs torque. Even though the compression dropped by .6 the later heads, carb, cam, intake and exhaust 'should' be worth about a 50-60 hp gain over the original 1969 factory parts. That's my opinion, I don't have solid numbers behind it though.
I run only premium fuel with Protek lead additive/octane boost in every tank. The last four tanks of fuel were one through the city and into the mountains up to 10,000 ft and it got 18.5 that tank. Next tank was 90% city driving and it managed 19.5 mpg. Next was city, highway, mountains and it was 18.6. The only all-highway run so far was a 225 mile run with the A/C running maxed out for about 60 miles and it managed 22.1 mpg. 60-65 mph. All runs had at least 'a few' romps. On the highway stay below 3,000 rpm or your milage will stink. With a 3.15 rear 3,000 rpm is 70mph.
Power wise (keep in mind 7,800 ft and a 3.15 rear) with no wimpy power braking, just off the brake and on the throttle from an idle to wide open it'll smoke the tires off the line through first gear. It gets a good 10-12 feet in second, no chirp in third. I have not had it on the track for 1/4 mile times.
It is exactly what I wanted when deciding to rebuild it. Much better milage, more power and it's as reliable as the sunrise, I'd drive it anywhere.
I could upgrade the ignition and get a couple more horses out of it but I grew up with points and have little desire to change it. If I was racing and wanted every .01 sec I would but I don't so I won't.
I think donsjave has a similar rebuild in his '70 AMX 390, 4-speed. Maybe he can advise if he did anything different and how satisfied he is with its performance.
Hope that helps.