I went from a 700- 208 combination to a 350- 203. The only problems that I faced were that my 3" pipes made it hard to get the tranny jack in place, the weight of the 350- 203 is dramatically greater, and the 208 had a slip yoke but the 203 has a fixed yoke so I had to get a new driveshaft (not to mention that the lengths were different). The 700 is electric, but the 350 runs off of vacuum so I spliced into a hose that ran close to the back of the block. You might want to run the new vacuum hose in through some fuel line or a piece of water hose to keep it from rubbing on it's surroundings.
