As per above, I would punt the Mondy on and use the profit for better stuff.

I run an ST170 lump in my mk4 Bonus and its awesome fun. The engines are really tuneable, plentiful and tough as well.

I've seen loads of scabby ST170's for under £500 these days. This would give you an engine, interior (as above door cards wont fit but I'm sure the seats would with a bit of work), 300mm brakes, 17" alloys etc.

Plenty stuff to sell to make your money back such as 6 speed box, headlights, IMRC (if working lol) body panels, clocks and the stock car boys seem to like the bare shells for racing.