You can't overboost a diesel. Well you can but it ain't like a gas burner where it's imperative to supply enough fuel to support x amount of air (approx 12 parts air to 1 part fuel under load). Until the EGT goes sky high, you can put as much air as you want into a diesel and it won't make a bit more power until you start putting fuel into it; then the power really increases.
RHB31 is probably the best option. It's tiny. But so is the little engine. Diesels operate differently in respect to the turbo. It will make presssure regardless of whether it's under a load or not, just the air flowing through the engine can be enough to make a few psi. On my little car, I can cut the ignition at the top of the hill (5 speed manual) at about 2500 RPM, then floor it with the engine just freewheeling, and it makes 5.5 psi. That's a gas engine. Diesels use smaller turbo's than comparable gas engines because of the RPM difference (diesel being about 1/2 the engine speed as a gas engine on average).
I've messed with this stuff for eons, don't know everything and never will...blown PLENTY of gas engines up, destroyed a few, salvaged a few, but never have hurt a diesel and they were all naturally aspirated in their original form, only change was adding the turbo, a pyrometer, and maybe an intercooler. A good example is my litlte Massey. The 1140 tractor was a 1.5L Iseki engine, made 30hp. The 1145 is the same exact tractor, same exact engine but turbocharged, makes 35 hp at the same RPM, quite a bit more torque down low (from the turbo). As I recall the ONLY difference between them is the manifold (obviously) and the pump is timed 0.5 degree differently, which amounts to basically nothing more than keeping EGT down. It does not have a wastegate. I've run it under a load and it'll make 15 psi in cool air, normal air 8-12. The old powerstroke diesels also didn't have a wastegate, they just made boost...the more air into the engine, the more out, so boost pressures would keep climbing until there wasn't enough fuel to keep boost from climbing. I think about 22 psi in stock form on a good day, 18-20 is the norm. Mine is an 03 that IS wastegated (more low end but less top end) and it's done at 24 psi, CEL at 25 for more than 3 or 4 seconds. Can it make more? Probably but that turbo is not made for it, most upgrade when they're getting into big numbers.
The RHB31 max shaft speed is 254,000 RPM....it's used on a variety of equipment. I have one out in the shop, tried it on a D722, too big, BARELY made 2 psi under a load, zero with no load. D722s' DID come with a turbo on some equipment but I haven't found any of them yet, turbo's or engines. I just want one to say I have one, don't need the horsepower or torque, it runs fine without it and that's probably why I ain't put a lot of time into finding a turbo and/or manifold.