I'm not an expert, but the reverse from one proaction sled should fit in another. They all use the same chaincase/dimensions.
As for a sleeper phazer. Sure it can be, but there is a limit to how far you can take a fan cooled sled and it's a pretty low ceiling. The 2001 motor is a little different than the 84-98 motor, but they are basically the same thing so the same info will generally apply. I had a 91. It was piped, ported, thinned head gasket rather than cutting, reeds, piston cut, flatslide carbs, and whatever else could be done and still trail ride it. I never dyno'ed it but the guy that did the motor work for me figured it was running about an honest 82 horse or so based on his experience with that motor. At that level I had to cut a gallon or so of 110 in each take to keep it from rattling the pistons apart and the compression was stiff enough that I couldn't keep a recoil in it. Sled was set up with some lightweight stuff and a 136x1.25" track. Here in the flatlands it was darn near unstoppable, but it wasn't very fast due to the gearing I ran. Doesn't even compare to my current ride.
Having done both things you are thinking of, if it was my $$ I'd try and sell the phazer and buy a bigger sled. The 700 class liquids are all going to make 1.5 times the power stock than your phazer ever will. Then if you want more power the potential is there to make more.
My two cents. Take it for what it's worth.