where there is a will...there is a way. Cost seems to come into play there, but this shouldn't be too bad...
I had a corrado that was automatic, that I swapped to standard trans... I had all passat parts and it worked flawlessly and was very smooth...did it in a weekend by myself at home. Short of a bruise on my chest from the old auto slush box coming down with no one to help, I was good to go. oh..and a broken shift box cable, but we took care of that...
Anyways...truth be told, the b3 assembly works the best with the b3/02a style parts and the o2j with the 02j parts, etc. Isn't the placment different on 02j's slave in the first place? Design and function will be the same, but you'd at the very least need to get the approriate lines made for it to reach from its location to the clutch master (combination metal/rubber lines), need to check for the total stroke of the 02j slave cylinder vs. that of the 02a one (don't want it too short to actutate the clutch finger, could eventually blow seals on the slave, or just not actutate the finger completely at all, or to long...), etc. The lines length in your case is probably the biggest problem.
Some things to consider. I'm sure it could be done.
Seems like the slave has always been the weak part in the VW system... even with the 02j MKIV transmssions, etc. people still seem to go through slaves alot! If I had my way, and could find all the parts....MKIII TDI tranny, or b4 tranny with the eurovans cable actutated clutch...
In simplier terms...what would I do? I'd try and run what you have... the b3 master setup but with the correct slave cylinder for the 02j tranny. The 02a one if I remember is slightly longer...the 02j one...more stubby. From there, its going to be fitting the correct metal/ubber line run from the master to the slave and from there, everything you'd think should work fine. I think attempting to use the b3 one would cause interference problems possibly because of its length...again, don't quote me... but its an idea... a hydraulics shop could possibly make the lines...or you could find the line on a parted mkiv possibly. I doubt there is a huge different in the length from the mc on the MKIV to that of it on the B3, corrado, etc. seems to always be some extra room to play with...
Don't know if that helps...or is clear, let me know if more detail is needed...
Joe