So far the v8 sounds like your best bet... surprisingly though the 43s are not all that cheap even though they are very old.. they are good engines though and if you can fit one with a custom turbo you will be pushing quiet some power... and turbocharging the 43s has been done in the past...

It would be pointless to put a c32 engine in there.. as the srt-6 engine is the same thing and costs less used... and if this is the route than just buy an srt-6 it will be cheaper and less consuming

And I have yet to be proven that the srt-6 engine pushes less than the 32s as all dynos have yet seen on either of these cars are just about the same and if there is a difference it is because of dyno set up and conditions the car was dynoed in..

Wish I could give some actually useful input, but I do not feel qualified enough to do so... your best bet is to post a similar topic on mbworld.org or benzworld they have more qualified people to answer your questions as many of them have much more experience with these engines than us crossfire owners do and there are many more engine modders out there than here...

But I would love to see your steps and process so keep us posted on what is going on as this is very interesting.