IMO, OS 12 TZ engines are good for weekend runs, reasonably priced... just make sure you run not too lean, probably slightly rich and check d bearings often, they tend to wear faster than d others.

in my experience, i already snapped 2 conrods tuning it to run at par with the fast guys...
probably my fault but usually running it lean u get an overheat... not a snapped conrod... waisted 2 sets of P/S on a lean setting...