I can understand your concern, however you've made one small error. The 500E engine is a stock MB engine. The fuel injection system was upgraded from the Bosch CIS, but that was an upgrade that, if i remember correctly, applied to the SL's as well. It was not built by, nor was it altered by Porsche. In fact, almost the entire drivetrain was donated by the R129 series SL, so the cost of reworking the engine and transmission should be identical to the cost of doing the same work on a 500SL.
And as Eric said, if you have the inclination, this could be an opportunity to go to an aftermarket shop and have some "extra" work done.
One thing I will warn you of, and I'm speaking from experience, modified vehicles and become very difficult to sell if you need/want to. If the car is a collector, it is usually easier to sell a good original example than a restored.
Just my 2 cents :-)
'93 500E black pearl/black leather; 89,000km; 245/45-ZR17 Michelin Pilot SX; 17x8.25 factory EvoII
'93 500E bornit(blackberry)/black leather; 69,000km; european delivery; 245/45-ZR17 Michelin Pilot SX; 17x8.25 factory EvoII
'88 560SL desert taupe/dark brown leather; 89,000km; Euro headlights
'87 190E 2.3-16 black pearl/black leather; 55,000mi; Euro headlights
'70 280SL white/red; 135,000mi (original); factory alloys; Euro headlights
[This message has been edited by yhliem (edited 10-29-2000).]