Steve -
I cannot see/tell what the yoke is hitting, but it is a solid stop, not just a snug interference. The yoke goes in about 2.5" before stopping.
Additional information to dwell upon: This same driveshaft and yoke slides in fine to the first transmission that I installed (jumps out of fifth gear). I found a Toyota 21 spline yoke on eBay and bought it just to play with. ($18.00). It is not the correct u-joint configuration, but it is a Toyota application, 21 spline, and the exact same OD and ID as the yoke on the driveshaft. It slides in without any problems!!!
And now to add more confusion to this never ending saga, I have an old junkyard Wxx Series transmission that I bought several years ago. Condition unknown, but it shifts into all gears. Both yokes fit it fine!!!
Rick: Powerline Industries has an East Coast distributor who I plan on calling this morning.