Welcome!
Following on to the above link -- you may also find some other useful reading on this forum by searching for "pinzgauer" and reading threads related to those vehicles. Several Pinz owners have been on here over the years and worked through similar topics as what you are contemplating. The Pinz uses this same engine family and is a similar size and weight. Quite a few members with Pinzgauers made significant engine upgrades and had good results and posted threads on here about what they did, which might be relevant to what you are considering.
Have you given thought to how you will handle the large increase in heat produced by the increased engine power? Keep in mind -- that is going to be the key to whether or not you are really able to use the extra power your engine is modified to make.
At the end of the day, when you are talking about a large and heavy vehicle like this one that can have big power demands for extended lengths of time, heat management ends up being the make-or-break part of the package.
You could pick any target peak HP number, but in reality you probably care less about the exact maximum HP -- you really care how fast your truck is able to climb a long hill fully loaded on a hot summer day. The peak HP number will ultimately have very, very little to do with that real-world result. It is perfectly possible that an LT45 with a stock, 100hp engine with a top-notch cooling system would get to the top of the hill AHEAD of an otherwise similar truck with an engine capable of double the max horsepower, but without enough ability to keep heat under control.
Those are all very much factors that you can successfully address, of course -- just want to add them to your list of things to start thinking about from the very beginning, as they are equally important to the final result as your choice of turbo, injectors, etc.
Glad you are here and sounds like a great project, look forward to hearing how it proceeds and let us know if we can help along the way!