you can change the length shorter a little if it needs to be if you have an old arc welder laying around. take grinder and grind down the weld around the yoke at the end of the tube and grind just the weld down until the yoke pops off the end of the tube
put a hose clamp around the tube where it needs to be cut and trace it with a tool that will scratch it good and then cut it off there and then pop the yoke back onto the tube real good and arc weld around it a couple or three times real good.
this is what i do when i need to cut a couple inches or so off the length of one
did it a couple months ago on a 1989 full size gmc van shaft for my 1991 s-10 2wd pickup so i could eliminate the two piece shaft because it was bent daamaged and wobbling bad due to frozen u joints
im about to cut down another one from the 78 chevy pickup i just got so i can run a 3L80HD trans in place of the dead original th350 9" tail because the 3L80HD is 34.5" long overall., 3" longer than the th350
just make sure you put the yoke in the same phase as it was originally so that the same u joint cap holes are aligned still.
and all will be fine
my s-10 has been doing great i tried to break the welds with launches and it wont and it drives smooth now yay
i used to be afraid of the idea of cutting and welding a shaft but actually its realy easy and works great
everytime i junk scrap cut up a vehicle for the shredder i save the shaft from it, they come in handy and have many times over the years!
you want the slip yoke to side into the end of the trans about 3/4 or 2/3 of the way
you can usually see the seal wear pattern line area on the yoke where it should be, and was at all its life, in which will be correct placement.
clean metal where its been inside the tail, vs. rusty metal thats not been inside the trans.
good luck