1500USD to build as much horse in a 360 as possible. What would you do?

I would say first.....get some pistons that will get you a good decent compression ratio....around 9.75 to 1. See what heads you have and the combustion chamber volume and figure it out. Then maybe a decently hot solid roller cam, if possible. This cam alone will probably set you back close to $1000.00, so maybe it's too expensive. You could do the porting yourself, with a Mopar Performance template kits (if they are still available). Also, zero-deck the block (since you access to a machine shop) and degree the cam in. You'll definitely want an aftermarket intake/headers too.