T5 swap & 351C

Something else is going on here. The 85 T5 and bell should bolt-up to any 65-73 289/302/351. You sure it's a V8 T5?

OK. As I understand thus far...
1. The pilot bearing is fully seated in the crank.
2. The throw-out bearing is fully seated on the output shaft back-stop.
3. The tranny & bell, lack by about 1/4" of fully seating.
Sorry, but have to ask, did you use a clutch alignment tool? Or, did I miss where it's not going together?

Good lists of things to check in this thread. I've installed a few manual transmissions and it goes really smoothly if you do these things.

1. Make sure the plastic alignment tool fits VERY easily. The clutch likes to slide downward and sometimes the tool is a little smaller than the input on the transmission. If you center the clutch well that will help.
2. I made two alignment pins using bolts with the same threads as the trans to bellhousing bolts. Cut the heads off and make a taper. This helps you to slide the transmission in straight and once the transmission gets onto the bolts they will support it. Make sure you leave the bolts long enough so you can screw them out once you put the top two bolts in.
3. Have the transmission in gear and slide a spare yoke into the back before trying to assemble it to the bellhousing. Then when you get the transmission almost all the way in, turn the yoke. This will help line up the splines in the clutch to the splines in the input shaft.

If you follow those 3 steps the transmission will always go in like butter with no wrestling.

Some people like to hook up the clutch and have a helper step on the clutch during the final push of the transmission. I'm sure that works, but my way you can do it by yourself.

What fly wheel/ clutch are you running
Also did you get the 351c t5 combo to work