Yeah $4k is a steal for an 89 turbo. I'm not sure the MO30 is standard, but I know it has the big brakes.
As stated above, the big things with any 944 are:
Timing Belt, Balance Belt, Tensioner Rollers, if you don't know its been done, do it first thing. Ask me about a broken timing belt. No Fun and $$$$. It was even worse for me, since I have an S2 and twice the valves to bend.
Clutch, I'm not sure if that car has the rubber center clutch(bad) if it does, expect it to take a premature crap some day. Clutch job on a 944 is no picnic. Expect 12-16 hours for a Porsche pro at $100/hour. We haven't even got into the parts total which approaches $1k if you want to do it right. When my clutch went out, I did it myself for the $1k parts total.
Water Pump. If the car needs belts, just do the water pump at the same time.
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Oh, and don't worry. The 914 is gonna keep its DD status. The 944 is for the girlfriend.
That table may turn when she leaves your 2.0 Djet ass standing still. An 89 turbo with bolt on mods can play with almost any car on the road.