For the guys much smarter on this than I………what would be the more "economical" route (in quotes because obviously money wouldn't be much of a concern with this): buy an existing C55 sedan and convert to wagon, or convert existing non-AMG wagon to C55 spec? I'm guessing the former, but I'm not sure what sort of chassis/structural differences exist between the sedan and wagon platform? Thoughts? Purely hypothetical, I have no true intent to pursue this, though I think it would be pretty cool.

 

The sedan and the wagon are pretty much identical. They're on the same platform and use like 99.9% of the same parts (except for the whole hatch business, of course). But you would have a problem fitting the block in the car as Mercedes was never able to fit a V8 into a 203. The front end of the C55 is actually the same front end as the W209, that's why Mercedes was able to shove a V8 inside.
I know the M113 will fit in the regular W203 front end, but if you want to use the stock fan and rad and refuse to adjust the engine mounts appropriately, you will be cutting into the firewall.

Look, a C55 conversion is really difficult and unnecessary. Get an S210 and make that an E55 if you're looking into a wagon. Otherwise, a C32 conversion would be much easier.

 

Yeah, inherent in the "take an existing non-C55 wagon" option was converting to w209 CLK standard front end. Certainly even that prep work would be in excess of $10k all said and done, even if done in the garage not paying for labor. Again, not really seriously considering this task, but I think I could do that much myself if extensive welding/metal work is not required (maybe it is?)………pretty sure I wouldn't be able to handle turning a sedan into a wagon however.

 

Why not just buy it from Germany for example? Shipping should be around 2k€ including the insurance.

www.mobile.de has loads of them for sale. It still would be cheaper even to fly there + ship it home than to try the modification route.