got the Yukon gear on mine best thing you can find at a good price! ($410 in Canadian money):)
try like i do....a local diff and carrier shop for good knowlage and tech that can guide you well! :)
found mine here: Unitrans.ca
87 R10 only got the TBI specific for that year, all other thing you need to know are in the range of '81 to '87 (even some '88 to '91 crew cab,blazer,suburban can help you too) ;)
Tejas Steel work make great motor mount not shure if can help you for your compressor location! ;)
https://tejassteelworks.com
Tejas SteelWorks Square Body GM LS Swap Guide
Position
The mounting position used in this outline is approximately three inches forward of “stock”. This position was...