Little 318

New is fine. I guess the 262 is it !
That'll work fine. Good choice IMO.

I wish I could afford almn heads too, would they make a huge difference?
Not really on a stock bottom end 318. The port size on a Edel. RPM head is not very good for a very mild 318. There very well sized for a 340 or 360.

Would I be able to swap heads in the future without pulling the motor?
Yes.

Also, drop the headers in the engine bay before you drop in the engine. Have a freind on hand when the engine goes in on each side of the car to hold and position the headers as the engine goes down. Once the engine is in the K-frame mounts and to the trans bell housing, the headers can be bolted into place.

This is easier than installing the headers after the engine is in. In a BIG way.

OH, forgot, the heads on the 318 now are fine as is for that cam. the most you could do for them is just prep the valve seat with a multi angle valve job and install a bigger exhaust valve.

IMO, since your awaiting funds for a bigger engine, wait on the 318 mods and save for the bigger engine.