If I were to do a n/a 3.2, I would just forget it is a Mercedes and do it like we did Chevy's and Ford's before there where stroker kits and such. I would build a mystery motor. looks normal on the outside, who know how big it is in the inside. I would max the bore and stroke. The crank would be offset ground, find rods and pistons that could be used. balance the whole assembly. You would need larger cams to support the displacement, and I would port and polish the heads and extrude hone the intake. How big can you go?

Well we know that some tuners are selling 6.1L 24 valve V8's and the three valve V8 is the same basic engine as the V6. This would equate to a 4.6L V6. If you wanted to keep it more simple get six rods, pistons and rings from a 5.5L bore the block, offset grind the crank, balance the assembly and you have a 4.1 Litre V6. I would call one of the many US cam manufacturers and have the stock cams re-ground. Isky would probably be willing to do this. You would probably need bigger injectors like maybe SRT 6 injectors.

If you wanted to play around like this you can get a 320 engine for a little as $300 - $600 on Craig's list. Usually an ML320 engine. Maybe you can also find a blown ML55 engine that still have six good rods and pistons? One key to not getting robbed is to stay away from people who work on Mercedes and find the reasonable guys working on american engines. It doesn't matter that the engine is Mercedes. the principles are all the same.

I just checked some bore and stroke number and the 3.7 is a 3.2 with stock stroke but with pistons and rods from a 5.0 V8 I'll bet this is how Startech makes their 3.8