X, J, or 308?

The above post covers it. T/A heads are exactly the same as other 915 heads, just have the intake pushrod holes machined in a different location.

Mild bowl porting will help the most with minimal work. But you need a good, accurate valve job without "sinking" the intake valves. The higher the seat, the better they will flow.
If any of the older heads need much work, like new seats, it can get expensive. New stainless nail-head valves that are back-cut flow better than the OEM tulip shape.
But if the work and parts start adding up too much, then you might want to price some aftermarket head assemblies, like the Indy/RHS MA-X. Gotta compromise between your budget and how much work the old used heads you find require.

Any of the heads you mentioned would work well. Just check for cracks. The 308's may actually make more torque because the do have slightly narrower ports. X heads only have 2.02" valves and are the oldest. 915's can have either.