The only way to safely boost the 6.2 or 6.5 is with the EFI since it takes into account the boost pressure to increase the fuel supply. The bad part is that i have been told that the 6.2 or 6.5 are not really a good candidate for really turning up the boost because the bearings are not quite as robust as some other diesels. I think years ago Banks had a turbo system for the 6.2 but it was limited ti about 2-3 pounds because Banks found out that any more and bad things started to happen the engine. I haven't kept up with all that so I don't really know where the whole story ended. The 6.5 gets away with a bit more boost because I believe they lowered the compression on the engine and probably some other things as well.
You can turn up the fuel on the 6.2 or even the 6.5 engines that came with the mechanical injection pump. I have one on my 6.5 and did turn up the fuel about 1/6 turn. The process is rather involved, try googleing for 6.2 diesel fuel injection increase. There are a couple of good writeups on the process. Not for the beginner mechanic or too faint of heart. Great fun doing it in a van. I don't think the results were worth the work, yeah it did do a bit better but not that much. Then again I kept it to the slightly gray smoke, not full black and wasting fuel.
Here you go this is one of the better set of instructions
Turn Up the Fuel on a 6.2 - 6.5 GM Diesel Mechanical Injection Pump