1975 360 bottom end power

IMO change that cam first. I have the Comp Xtreme energy and even though mine is probably bigger than what you need(284/296) it still maintained a great low end even on my low compression 318( I am building a 9.75 SCR 318 anyway). You could go with the Comp XE 268 that a lot of people seem to recommend.

Torque converter can help a lot as well, as long as you get one setup for your application.

What is your rear end gear ratio? Moving from 2.xx to 3.23/3.55 will help a lot.

Cylinder heads: Be careful in this area, larger combustion cambers will lower your compression and decrease low end, so will increasing the runners and valves themselves. So IMO don't mess with changing cylinder heads unless you know the combustion chambers are smaller and need more compression.

Long tube headers should in theory improve things across the board, but are a PITA to install, and on my nearly stock 318 did next to nothing...(seat of the pants and track), but most likely much better gains depending on the cam.

Ignition timing: A little more timing will help, could start with a better than stock distributor.

Intake and Carb: What do you have here? I think the stock 360 4 barrel stuff should be pretty good for low end, maybe even midrange.