I have a '97 K3500 with the 6.5TD that has been a complete nightmare as far as keeping it running right. It has been one problem after another, and I have just about gotten to the breaking point of junking it instead of spending more money on it. seems like I am spending a couple to three thousand a year just trying to keep this POS running. I can pick up a complete military surplus 6.2 minus the exhaust manifolds and starter with less than 25,000 miles and guaranteed for a year for less than I can have this injector pump built. What is involved with putting a 6.2 in place of a 6.5? Will it be a bolt in replacement or will other mods be needed? Any help will be greatly appreciated.

The military engines have 24 volt electrical systems. The injection pump will have to be converted to 12 volt. A 6.2 injection pump is marginal to use with a turbo. Same for injectors. A different flywheel will also be needed. Not really a cheap thing to do either.Many other things have to be changed to convert to mechanical injection.
You gave no real history of what problems you had previously and what the problem is now.
A decent rebuilt electronic injection pump can be had for $450-600. Have you priced a flywheel?