First couple times out it'll be in the 12's like that. I'd put 26" tires on it at the track to maximize gear (or find a 456 center section and keep the 28's) and shift it at 6800-7000 to see what it likes..might see a couple high 11 sec passes like that.

Its heavy, a 4-speed, and has light gearing and a smallish~ cam.

You would see solid 10's with an M1 intake, 600 lift and 456's and 200lb weight drop easy IMO

Also read/search anything member Big_Squeeze has said about getting those cars to hook