Search Pirate, that's where I got the one I had.
As far as what you need, you will need the fron half of the 231, you get a plate to weld onto it. You trim to fit the plate. Also get another shaft to mate the two.
Gives ya good low gear, but, I kept breaking mine.(the 231 case part)
Yeah I found a great write up on there he used a 241 gear in it....but not really sure on how to go about doing it...I've got both a 231 and. 300.....so I'd like to see if what a shop or someone would charge to do it?
Only thing you need to do as far as machining is cut the front half(cut off the front output part. Easy enough to figure where to cut, just put the plate from the kit on it and mark it. You will have to have a block off plate to fill in the hole where you cut the out put shaft area off. From there, it's all nuts and bolts. oh, and you have to make a shifter for the crawl box planetary. Some kits come with one, some don't