I have an old postal truck that originally came with a 6.2, and the previous owner said that a 6.5 was put in some time after 1999, because the casting numbers on the block end with a "9" which refers to the last digit of the year it was made; i called GM parts division and they told me the same thing - it has to be either 1989 or 1999, and since the truck is a 1987 it probably did not get a new engine in 1989. So by this logic it was *probably* (hopefully) 1999, which would make it a 6.5 n/a.
So here is the question - the same person also told me this is a 6.5 "replacement" engine, made specifically to replace 6.2's, and that it is somewhat different than the 6.5 n/a engines that come stock with other trucks. And it is of course different than the turbo's as well.
Does anyone know if this is true? That would mean there are at least 3 variations of the 6.5, and i have heard there are even more than that but i don't know if it is true.
Mainly i would like to know this so when i am looking for parts i know what to tell them - usually anything that fits a 6.2 will fit mine, but so far i have only replaced little things like thermostats and filters, etc.
Any advice greatly appreciated.
thanks,
Paul

Most bottom end parts are interchangable. The confusion comes when it is time for things like valve replacements or precups because there are a lot of different part #'s. If you have a late model block, it also probably has piston oil cooling jets, the easy way to tell is with the pan off, the outer main bolts are a smaller size than the inners. The oil cooler line ports are also larger than the earlier engines. I personally wouldn't worry much about it, since all of the bolt on parts are interchangable, just run it and ask for parts for your year of vehicle.:cool: