I would think that it wouldn't be too difficult to convert linkage pedals to hydro pedals. The only real difference (iirc, been a while since I looked at hydro pedals) is that the hydro pedals have a stud (at about the same height up the pedal as the brake booster plunger on the brake pedal) for the master cylinder push rod.
Have you looked at any of the aftermarket hydro stuff? I have a 4 speed truck right now that I plan on converting in the future using an aftermarket pull style slave and matching master cylinder. About $100-150 worth of new parts. Build a small bracket to mount the slave on the tranny and modify the fork to attach to slave. Then drill and mount the master on firewall and connect to linkage style pedal. Easier than digging up factory parts and doing the work to swap bell housings and all the other stuff.
I also have a friend who built a bracket to mount a factory style slave on a manual bell housing. Don't have any pics of it but just so you know it is possible with a little imagination