I found out the hard way today that a 1.9 with a GT bell housing and clutch release arm will not work in a Manta. The arm is too long and hits on the trans tunnel area on the drivers side. Once I took the trans out and then the bellhousing (what a PITA with the engine in the car) I could see the differences in the 2 bellhousings. I would think that a Manta bellhousing and clutch arm may work in a GT, if that were the swap you were doing, since it would be protruding less than the GT's original. Next weekend I will get the proper bellhosing put on (and the front stabelizer bar put back up- it needed to be dropped to get the bellhousing out with the engine still in the car). I think the right lower trans bolt is even worse to get at in a Manta than it is in a GT. Ended up putting a stubby 15 mm box end on the bolt, and then prying that wrench forward with a regular box end wrench pushed off of the trans to keep the stubby from slipping off the bolt head as I tapped the stubby with a hammer to break the bolt loose. Add to that the exhaust pipe right there in the mix and it's a joy!
Good news is (I keep telling myself this as if there is any good news!) is that I'm right there as if I were just replacing the clutch with the engine in the car and it just needs to be put back together now.