727 TC Installed - Probably Wrong...

another possible cause (this is assuming you DID seat the TC) is that one or more of the TC bolts were never tightened enough - - it only takes one. I would take the starter out (or at least pop it out of the hole enough to disengage it) and take the TC dust cover off and see if any of the bolts will tighten any more. You'll probably only be able to get at two of them - if they won't tighten then you will surely need to loosen them. If this is what it is, it can be very problematic trying to get all 4 tightened properly - tighten one and the other 3 (if slightly loose) will inevitably hit the back of the block because they are now sticking out too much. You'll want to pull a few spark plugs to lessen the compression in the engine as you are going to have to turn it by hand with a socket (at least, this is how I did it when I installed mine). Engine break away should be around 60 foot pounds and the crank bolt - IIRC is torqued to 125, so you can turn the engine forward or backward depending on what you need to do without loosening the bolt. You have to futz around to get each of the TC bolts at about the same looseness - while also pushing the TC itself backwards into the transmission.. it's a "dance" and can be frustrating.
I'm betting (and hoping for your sake) that you got 3 out of 4 properly tightened and the 4th one is up behind the engine and catching on the block - totally resolvable - just not a lot of fun.