Driveshaft help

[kcstreetracer]

I have a lwb 68 c10. I had the motor and transmission out, now putting it back in and the driveshaft will not go back on the rear end. Slip yoke is bottomed out on transmission and its lacking a inch or so to go back on the rear end. The motor mounts are bolted in and good. I've tried prying, rotating rear end, jacking up on tail shaft and can not get it back on. Am I missing something? Can I just get a shorter slip yoke? I feel if I do get it back on it may push in on transmission to much if it flexes