ok, i cant do this yet but i am getting as much research done as possible before i do. i am going to build a custom rig and was going to put a 302 in it, then mate it with a t5 because i would like to have a manual tranny. what reliable transfercase can be mated to the t5 that has a good low range and possibly a doubler option for a even lower range. i was thinking the 231 but does that have any doubler optins? and are there any other forums or websites that have good info on this stuff? thanks for any input.  

The 231 is aluminum. The doubler will have to be somthing like a Klune-V, about $3,000. for 231. The 231 has a 4 to 1 kit but is expensive. Advance Adapters is a good place to look for adapters. Why not concider the Staks or Atless transfer case the new three speed Staks and 4 speed Atless go for about the same it would cost you to buy a case,rebuild it and add a doubler. Maby even cheeper. You can use a 205-203 doubled up case. Get a older top loader with at least a 6 to 1 granny low. I like my t18. Put lower gears in the axels to. I use 538's in my Dana 60's.   

what is the top loader? is it the t18 and 19, like the 18 you mentioned? and i have been considering a stak or atlas. how nice to have 2 lows and have it be compact. i may still consider that. but is there any better of a transmission that is reliable, a 5 speed, and has low first gearing? what is the transmission in some super duties that has the extra low first gear. i also want something that would be good for highway driving. thanks agian for the info.