I went to salvage and got mine but that was thirty years ago. Wish you luck.
That's what I did, but that was nearly 20 years ago. The wrecking yards I used to go to have all either closed and gone out of business or stopped carrying parts for our old trucks. I haven't found a local yard with anything older than 2000 for a while.
I had to drill through every single spotweld to remove the upper cover in order to get ready to swaps trans (we could not get to the bell housing bolts from the bottom) GM used 28 spot welds in less than 2 feet, I kid you not. I'm using caged nuts in 6 locations to fix in place and double sides tape in between those. I had to drill through each one with a 1/8" bit then a step drill, that was some tough metal, burned up or wore out a spotweld cutter. The new repop fits well. .
Those spot welds were a PITA!
Previous owner swapped out the 3 on the Tree (low hump) for an SM420 4 speed (high hump). Bugger didn't change the hump. He just screwed some sheet tin over the whole works and called it good. What a nightmare!
Plenty more wrong with his work, but that's another story.
Parts can be found. It's a pain, and it may require shipping, but they are still out there. The back half is easy. Nothing to change there.