big block or small block

If you already have KB107s installed in the 360, then you are well on your way to 350/400hp, or mega-SBM torque. All you need are closed-chamber heads and the appropriate cam. If you wanna spend money; I highly recommend alloy heads and pushing 185psi Cranking cylinder pressure. The hard part will be not to roast the tires all the time.
A 222 to 226*(.050) on a 110LSA cam will be happy with 3.23s and stock stall. So you save money on those, to spend on the heads. At the price of gas today, I highly recommend a smallish Solid-Lifter cam, but that will cost you adjustable valve gear.

The BB in this case, and IMO, will overwhelm the biggest street tires (255s IIRC) that you can fit into the stock 73-Swinger tubs, and so you can never really floor it in first gear without tirespin. Maybe not even in Second...... What happens when you pull out, on the hiway, following Gramps at 55mph? Do you really want tirespin on the 3-2 kickdown, in this situation? Are you gonna remember to ease into it?
In my experience, by 55mph, a 360 with 3.23s, is already torque-challenged in Second gear up there, so this should not be an issue.
Just something to think about.