3.6 Engine Advice Please

[quickrich12]

Hi, this is my first post so be kind!

I recently bought a 2003 C4s with an engine knock which upon stripping turned out to be a big end bearing chewed up destroying the crankshaft. Unfortunately I do not have an endless pot of money to repair it and a used crank is impossible to find (in the UK anyway) so I have been trying to work out my options. This is the best I have come up with so far and would like you clever people to tell me if it will work or not.
Fitting a 2.7 boxster crank and crank carrier with boxster con rods and the 3.6 pistons. By my calculations this will turn it into a 3.4, but my biggest concern is I think it will raise the piston crown by 0.5mm, is there room for this? The other option is to use the 3.6 con rods but I think this will lower the crown 3mm, would the compression ratio be too far out? Please let me know what you think, thanks.