Don't know where to start so I'll start somewhere

With a 1990/91 would you rebuild the engine, upgrade with aftermarket heads, add newer auto-tune EFI

or

Look for something like a ~98 or so donor truck and get the newer 4l60e and Vortec heads and rebuild all of that?

Or other suggestions.

My odd thought was a 4.3 with turbo...

 

Intended use is missing from your question. What is your goal? Budget? Condition of your existing engine and trans? Vortec heads will bolt onto your 90/91 block but you must use a vortec intake. Are you doing the work yourself or paying someone?

"Should I rebuild my motor and trans or get another used one?" Without any more details is impossible to answer intelligently.

 

Best bet would be to swap an LSX and 4L80E tranny, regardless of what you want to do with it. Better power, economy and emissions. Otherwise, nothing wrong with building up what you have. Pretty easy to get 300 hp out of what you have but you'll suffer on mpgs.

 

I stand corrected. Thanks AJ for the intelligent answer.

 

I see your point but just asking in general. Just a good motoring setup with some towing. Early broad torque curve that is hit without getting into the really high RPM's.

Budget friendly is nice but I don't want to be pound foolish, penny wise either.

The next question is when do I pay someone else to do (any machining certainly). I can do general work. The biggest things I have done is change master cylinders, rebuild calipers, change bushings out of steering components etc...

 

Any particular years I should look at for a donor. I saw someone make the recommendation of getting it out of a 3500 van as most likely weren't setup for towing.