I see you have a 108, which is the ONLY wy I's consider it. The 518 is the same externally as a 727 until you get to the tail section. That tail section is longer (big problem in a 100) and fatter. They require cutting and welding to fit in muscle cars, due to the fatter tail. It interferes with the torsion bar crossmember. Since the vans have the trans hanging down, there will be little to no issues.
1993-94 is when the lockup torque converter was added.
You can decide if you want the added MPG and slightly lower RPMS on the freeway (approx 100 RPM) with a stock stall speed which is best for a stock or mild build, or go with an earlier non-lockup trans and be able to use any aftermarket torque converter with higher stall speeds and more strength. That would be more suited to a more radical build, along the lines of a street/strip car.
The weak link is when the trans is in OD and you hit the throttle, the 3rd gear clutch pack ends up between a rock (the tall gearing) and a hard place (engine torque). It is best to use a throttle switch or vacuum input to kick it out of OD. If you run a Torque Converter Clutch (TCC) for lockup, it is nice to have a switch for that too. Most use a brake switch input for this, just like a cruise control.