It would be cheapest, more powerful and more reliable selling the GSi and buying a VTi-R.

A B16 head on a B18 block will only marginally raise the compression from the stock 9.6:1 to just under 10:1. You'll then need a new computer and piggyback to add vtec control and A/F ratio adjustment to allow the car to actually run properly. You'd still be stuck with a 4.2 final drive GSi gearbox too.