I wouldn't base your motor choices on cooling issues. Install whatever engine you desire along with the proper sized components to provide adequate cooling. In my opinion, you should be able to install a big block and be able to maintain normal operating temperatures, so long as everything else matches cooling requirements.
Whichever size engine you decide on, will require the proper size radiator to keep it cool.
If your ultimate goal is keep a radiator sized for a 6 cylinder, then you shouldn't go any larger than a 6 cylinder.
The engine compartment on a Task Force is huge, your engine choices should be unlimited. It is a fact that larger engines require a larger cooling capacity.
It's no different than sizing a home to an air conditioner that you may already have. A one acre lot will provide ample space to build a mansion, but you're not going to cool it with a 110 v window unit.
Good Luck
John
