TKOPerformance wrote:

A flat top in a 331 and GT40P heads should end up about 10.5:1.  That's too much for the type of engine you are building.  That much compression with a baby cam is going to be a mismatch.  I would look to run a dished piston to get compression more like 9 or 9.5:1.  This should also make valve clearance a non issue. 

 
Yeah that makes sense… I still need to figure out what gear to put in the rear too.

In my 69, I built a 331 with flat top pistons and 60cc Edelbrock aluminum heads. I used a stock roller cam from a 1990 HO Mustang.
It runs great, idles smooth, doesn’t lug down on the hills and runs on REGULAR GAS.
Set up the way it is, it is not the most powerful engine on the planet, but it is smooth and has lots of torque for pulling fifth gear on the hills. It is doing exactly what I designed it to do. It has a single plane “no name” aluminum intake, 600 Holley and a Pertronix distributor, hipo exhaust manifolds and 2” exhaust. 
I put 3.50:1 traction lock rear gears in it.  Tranny is a T5.

This car was built specifically for the annual BASH trips, so I wanted smooth power and regular gas. It gets its first road test tomorrow when I drive 200 miles from Canyon Lake to McKinney, Tx.

So far, I am very happy with the performance.  If I ever get tired of the performance, all the internals are there so a cam swap and headers would really wake it up. But, as far as drivability, it beats the heck out of the 427 in my 66 that has a bigger cam.

I need to tear the explorer 302 down soon and see what I got.