can I pick up a used posi pumpkin on ebay or whatever and install the posi in my non posi pumpkin?
I have a 3.08 open rear, want to upgrade to posi. can I pick up a used posi pumpkin on ebay or whatever and install the posi in my non posi pumpkin? also, I see i can buy out of say, summit or jegs, a posi unit. will this bolt into a non posi pumpkin or will I have to find a posi pumpkin to put the new parts in? If I stay with a factory posi I pick up whereever, are parts still widely available for rebuilding the old posi unit?
Maybe. They are offered from time to time but because they are so rare and highly prized by 1953-'62 Corvette owners the price for a factory "P" case runs from $1,500 to $2,300 to successfully bid on one. If you buy one yes you just bolt it in and go.
also, I see i can buy out of say, summit or jegs, a posi unit.
Provided the parts that they are selling are for your rear end, and not a 1965-'72 rear end which also had an 8.2 inch ten bolt but used entirely different parts.
will this bolt into a non posi pumpkin or will I have to find a posi pumpkin to put the new parts in?
Once again this depends upon fitting your rear end. You have a Salisbury drop out rear end as opposed to the same size Spicer rear end where the gears stay in the case and you access them through a an inspection plate in the rear of the case. The aftermarket makes parts for Spicer rear ends that work inside an open differential case to convert it into a limited slip or posi. They generally use gears instead of clutches due to the lack of space but work as well.
If I stay with a factory posi I pick up whereever, are parts still widely available for rebuilding the old posi unit?
No. They were not widely available when these cars where new as there where no posi's sold to enhance performance. People back in the early sixties, if they ordered a posi, bought it to survive driving in winter snows. So only a traveling salesman would order that option normally. Since there are very few traveling salesman cars surviving today (they were usually driven into the ground, and then scrapped), there are very few posi cases surviving. The posi case is different from an open case. It has a "P" cast into the drivers side of the case to identify it.
Another option is a Pontiac-Olds rear end which was sold as a high performance rear and had a lot more posi units sold for it than Chevy had. The Olds/Pontiac rear end is uncommon today because racers used them up in the late sixties as they were extremely strong and rarely broke unless you where trying to pump 2,000 horsepower through it spinning slicks for a full quarter mile.