a dual master cylinder should be on your mind no matter what unless you are doing a numbers matching or completely stock rebuilt.
some have done a hydroboost and mounted the master and booster back on the frame a bit further. used the stock master location as a run through "bushing" sort of and added length to the pushrod to meet up with the booster mounted further back. maybe a possibility for you too if you have some fab skills.
here is a set up or two (if you scroll down some) with pics so you can see how it works and what I meant. these are the task force trucks but you could prolly make something work along the same idea. you do need a power steering pump to make them work but they are quite a bit smaller in diameter than a vacuum booster and it can't be rocket science to fab up some brackets for the pump on the stock engine. there are probably mounts made if you google it. system would mount under the floor and use the stock pedal assembly so no monkeying around with pedal mounts and a firewall mounted booster. it would give clearance for other stuff under the truck.
just a thought.
http://67-72chevytrucks.com/vboard/s...d.php?t=498494