Try this link. www.tomsdifferentials.com/cat126.htm
It seems late 12 bolt spiders fit right in but you'll need modified 12 bolt axles. However, there are at least 2 different types of side gears and I'm not sure which carrier will fit the 12 bolt ones. I replaced the drop out in my '55 1st series with an early '60's 3.38 and the side gears were different. I had to mix and match the parts a bit. I hope this helps.