If you are not apposed to damaging the transaxle that is in there further, since you have a replacement, and the other one is locked completely and you cannot force it to move without risking your clutch,c/v's or starter/gears, you can guestimate where the coupler bolt is pointing and choose a spot in the transaxle big end aluminum casting, then drill a new hole to slip in your socket;extension.. if it's pointing up and you cant get at it with a socket/extension, you can dismount the entire torque tube and assembly at the front of the car and tip it down slightly to gain acces, at the risk of damaging your pilot bearing/flywheel/clutch. If that isn't an option, cut a big access point into the transaxle bell housing, like a BIG 5" wide hole, to fit your hand/arm or small leprecaughn in there to reach in and around to get at the bolt to unbolt the coupler.. Here is an image, compare where the coupler square edge is pointing etc.. the side that has the bolt on it and to the extra transaxle, the space you have around the underside of the car for fitting tools, grinders etc.. to help decide where to make the new hole, if that is what you do...
source vwhammer from motorgeek.com
motorgeek.com :: View topic - Porsche 944 Transaxle?
It's an option, but it would be better to get it to rotate so that the bolt is pointing at the access hole. PS, have you already checked the parking brake?
Releasing the clutch and rocking the car back and forth with the help of a couple friends might help move it. You can guess where the coupler bolt might be pointing, then mark a dot of tape, on the rim of your lower crank pully, so the tape is on the side of the pully where you think that the coupler bolt might be pointing at, then getting the whole thing to turn, hopefully without the clutch slipping as the coupler is 1:1 direct drive from the crankshaft via the clutch disc... Once you get it moving, watch that dot of tape, get it pointing in the direction that the access hole is at on the bell housing, then check to see if you can get the bolt on there.. Thats probly only possible if the trans/cv/tires are still bolted on with the car on flat ground... set the brake before you climb under there to look
I don't think it's a good idea to crank the engine over with the starter or the front crank pully bolt to try and break loose the transmission.. The cv axles are easier to replace, and designed to flex a little and give a little, rocking the car via the tires is going to effect the transaxle FIRST, then the engine, and the engine is only compressing air while it turns, not metal to metal like the starter ring gear..