Next size up from k03 for a low mounted turbo??

[Tintin]

Without knowing the budget, mechanical skill, equippment and what part you have on hand, it's hard to tell. for low mounted turbo, there's nothing to replace the k03/Gt15.

The easiest bolt-on swap is the K/14/T2, as long as you have all the parts from the donor car, of course this will require some welding for the downpipe.