What turbo do I need?

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Sorry if this is in the wrong place but I need to replace my turbo and am wondering what route to go. I have a 1994 12v cummins with a #8 fuel plate, 4 in straight pipe, 75 hp injectors, bored 40 over. Colt cams big stick, 60 lb valve springs, 3k governor springs and timing at 16.5. Has a 5 speed and full ceramic clutch. All of witch have been swapped into a 76 dodge powerwagon and it is intercooled.
My question is I have a hx35w and its passing oil. I was thinking of doing a hx35 hx40 hybrid when I rebuild it. I am wondering if this will be enough turbo to get me around 40 psi of boost. I have also been thinking on the lines of a s300 but not sure what sizes to go with for the best towing and spool time. don't really want to spend the money either. I don't want a lot of lag because I live in Colorado mountains and need to be able to stay in the power when I shift with a load. Or am I just needing to do a whole other turbo than I mentioned?