Replace Sportomatic?

I bought a 1971 911T with Sportomatic with about 105,000 miles on the odometer. The vacuum operated clutch diaphram apparently has been leaking badly for awhile. The transmission jumps out of gear in third and grinds in the other gears. I would like to either rebuild and convert the Sportomatic to manual transmission with a pedal operated clutch, or replace the entire Sportomatic with a manual transmission and clutch. How difficult would these options be? If I replace the transmission, which one should I look for to achieve the easiest conversion? Any other suggestions?