Absolutly everything you need to know is here
http://www.shoptalkforums.com/viewforum.ph...b19f03e8d6ed004and here
http://www.tunacan.net/t4/ click on the links in the orange right colum.
Joe Cali still has a conversion booklet for using the T1 shroud you can read about his conversion at Tunacan under the cooling with T1 alternator conversion
http://www.nextgen-usa.com/ to buy his manual
I put 1 in my super beetle with a DTM , ran good and lots of torque. Be prepared to spend some $$$ Mine was $6800 cdn for about 120 hp. If you think you can do it cheap because you have the motor then be prepared to do everything yourself. You will need to fab up an exhaust, and a shroud. The 210mm flywheel gets a T1 input shaft needle bearing pressed into it, other than that it's a bolt in.
If you can do fab work on the shroud and exhaust , the motor is in good condition( running and not needing a rebuild), and you have free T1 shroud parts, and 2 sets of T4 cooling tin for cutting up. You only need to get a shop to ream and press in a bearing flush to the engine side of the flywheel. Make sure you have the T1 press in nut from the case above #3 cylinder, or you won't be able to bolt up your engine to the tranny, it has to be installed into the T4 case.
You can do it if you have everything, and are handy, or have a buddy that can fabricate.
Make sure you don't grind the transmision case with a grinding wheel, use a carbide cutter, or you may find out that magnesium dust is explosive.
Read the web pages above they answer every question you could possibly have.
Kevin