Thought I'd chip in
As Rob says, if you reverse the rear cradle it will push the engine/trans forwards about 2" and you won't have to cut the fenders. You will have to cut off the front mount and either relocate it or just use a berg style mid mount. Obviously, you can only do this if you are running IRS. You can shorten the oil pan about 30mm and still top up with the stock oil volume as the crank is way above the sump. Any more and the oil filter and exhaust manifold are just as low so there's no point.
With a custom frame, I would push the engine forwards and up as much as you are happy with, the limiting factor being the CVs you are using. This is what I will be doing shortly with my G50/WRX in my 1303 cabrio.
Rich