A 1988 Turbo S or 1989 Turbo 944 will easily make 300rwhp with just a MAF conversion and new chip using stock internals and the stock K26/7 turbo.
Stroking the engine from 2.5 to 2.7 and upgrading the turbo to the K27/7 will get you to 400rwhp (with a few other tidbits). This is without running at ridiculously high boost. It is streetable and reliable.
Overall, it will be cheaper and with no fabrication. Also looks stock when you lift the hood, so no issues with insurability (ie. heavy modification, engine swap, etc.).