Will a stright six from a 1964 chevy truck fit a 1986 Caprice Classic with a 305?

You can modify it to work. Just some customization with the motor mounts and make sure you have enough clearance. You will have to modify the driveshaft and the cross member.

Thank You!

Yes as above answer. The old Chevy 6's are a taller engine. Engine to hood clearence might me tight.

come on those heads are a dime a dozen....replace it..

Messed up 305 cyl head, how? Most cyl head shops can repair them, replacing rocker arm studs, even welding cracks, & expensive. Easier to replace it from from a salvage yard, because the low compression / small valve heads are so common. 307's are the same too.