I Have a situation

It sounds like a few mismatched components. I didn’t see where you said what exhaust you have. You mentioned stock 273 manifolds but never mentioned if the stock single exhaust was still in the car? What rear gear are you using? 80 mph trap speed is low. Are you still on the gas or did you lift early? You mentioned you are spinning at launch. There must be some torque there. Do you have a limited slip rear axle? Are you doing a burn out? I have launched a peg leg 1967 Dodge Dart with a 340 into the 13.8 on 215 70 r14 tires and 3.23 gears. A lot of rubber on the track and 2 burnouts. (One for each wheel).
What altitude is your track at? If you are in high altitude your car won’t make as much power. I used to run at 2 tracks. One close to sea level. The other at 3000 feet. I picked up .5 just from going to the lower altitude.