There would be nothing easy about fitting an L20 crank into an L16 block, and it will cost you some money.

and 87mm is the upper limit for a good L16 block. Would be much better at 85mm for a turbo engine.

I don't really understand why you want the L16 stamping, 1.8 turbo is no problem in a 1200. Save the headaches and money and just use the Z18. Or if there's some new rules about capacities and you really have to use a L16 block, just bolt the Z18 internals in there.