i have 489 case open... how/what do i need to make a sure-grip?

i have a 489 cased center section in my 8.75. it is a open, and i am sure it has a highway gear. what do i have to replace to make it a posi unit, and i am looking to make it like a 3:73 i think woud be nice.

any companies out there that seel a full unit? or ..if i buy all the parts to put in my case, do i still need to send it all to someone to set it up or would it be a drop in thing?