that 3.8L conversion in 'excellence' was done by sportec. and although it did not excite the auto-journalist, i think seal grey on anthracite rims is the best color combination i've seen yet. may have to copy it
unfortunately, swapping the 996 GT3's engine is no easy task. i've read up on a few german tuners who have done it and there are a few issue to overcome.
1) the GT3 engine is based on the dry-sump GT1 derived block (same block as the 996 turbo and GT2). as a result, the tranny in any wet-sump M96 block boxster does not mate up. a GT3 tranny would need to be acquired and swapped in with the pin gear modified to reverse the direction of the output through the gears. some track car conversions who have done this swap simply ordered a custom race tranny from hewland.
2) a new intake manifold would need to be fabricated as the GT3 manifold is too tall to fit in the boxsters engine bay. otherwise the folding top storage area would need to be banged out to allow room, which was done on a couple track conversions.
3) there are also location issues with the dry-sump system itself, which require some plumbing innovation.
damn shame this conversion is so cost prohibitive, because it would make one hell of a car with a bulletproof engine.