What GLF5driver said
I have recently bought a very nice GIV to add to a Challenger in the fleet.
Gulfstream is a great product with outstanding support,
It took me 2 months including walking away from 3 or more aircraft that looked good on paper, to nail it down and that is after around 9 months research and I actually know what I'm doing.
Beleive me the GFC still reverberates through the market and has produced a whole set of new challenges to the used market, some potentially quite nasty to add the usual others in the purchase of used aircraft particularly the older ones.
Unless you only want to operate in the continental US forget GII. The Stage 2 engines are the problem. There is an STC for Stage 3 mod but that only puts off the inevitable and is not generally accepted outside the US. In any event you would only be making someone else's problem your own.
Unless I am mistaken, what you seem to be looking for or at least the expectation is going to cost towards USD 10m and you need to budget min USD 1m pa to have it standing out the front plus DOCs, AND be capable of writing a cheque for USD1m at the drop of a hat for things that will go bump in the night. If you can't meet that It s the road to perdition.
it goes something like pay now or pay later.
Good luck