I took the disc brakes off a 1978 concord. I used every thing but the master cylinder. I rebuilt the front end and converted to disc brakes the same time. on the 1972 Gremlin. my 1972 Gremlin is a original 304 3spd car. the 3 spd has problems I need a clutch for it and the shifter is worn out as well. so I am going to change it over to a 727 TF. I can't get a new clutch for it nor a shifter. they don't make either one any more. A 6 cylinder bellhousing will work AS long the 6 cylinder is a 1972 or newer. But the bellhousing is 6' deep where a V-8 one is 8' deep. there are exeptions the 1972 Gremlin V-8 has the 6' bellhousing with a T-14 which is a little bitty tranny. which my car has. I think from $ stand point you are better off with the automatic. My 1976 Gremlin has a 904 TF. which I had no problems finding parts for. (the 904 was completely rebuilt). My 2 cents worth. Tom 72Gremlin with a 360 3spd. 76Gremlin with a rebuilt 904.