Track car engine options?
 

After building my wrx blob for the last 12 months into a decent spec'd track car, the bottom end started knocking.

I dont want silly power, somewhere around 350 bhp, any sensible ideas/ best options to getting back on the track quickly and more importantly as cheaply as possible?

2.1 stroker in a semi closed block - or forged 2.0 semi closed - no need to go closed deck at that level - or just drop a known good sti lump in.