Firstly you are running 160bhp not 200bhp and 250ftlb max not 300ftlb at the flywheel.

250bhp+ is not possible from this engine without doing damage to it.

Realisticly you can part ex it for a 20v version or you can do an engine conversion with the 20v version otherwise its free flowing induction (to reduce smoking) derestricted exhaust, extensive mapping and you will be around 190-200bhp and the 300ftlb. It uses a VNT turbo for a reason, change the turbo and you reduce low down power.

It is not possible to get 64bhp and 75ftlb from a remap alone unless Alfa are stupid....(which they are not)