Agree with Banshee.
Sell the 64's to someone restoring a 70 FB/GTO 455.
E-hds will make more power and run cooler.

Example,
Nothing exotic.

455 with box stock E-hds, RPM intake, RAIV cam, 1.75 headers, ETC.
Can cruise around on 87 octane, and add 92-93 for the track.
Average 11.90 to 12.00 @ 114 mph in 90 degree heat. Faster in good air.
Only thing have do is put on a set of slicks and a helmet.

Oh ya.
That's with letting the TH400 shift itself with 3.42 gears.