Those are interesting symptoms.

Here's a quick and easy way to verify that your transmission input shaft is not bottoming out in the crank's pilot hole.

Try loosening the 4 bolts that hold the transmission to the bell housing and see if the transmission moves back by itself. If a gap opens up between the trans and the bellhousing, you likely will have to cut/shorten the input shaft.

I had to shorten the input shaft on my 833 to allow it clearance from the bottom of the pilot hole in the crank.