though my full race 230 is severely intake limited right now, and as such will only spin to 5200rpm, I can help you with the mechanical part of your 6000rpm question....my engine uses the middle spring out of a triple spring set from Scneider, used, out of a small block Chevy sprint car engine. Approximately double the installed seat pressure of a worn out stocker.
Cross drilled crank is a must for high rpm use
you need to speak with Earl Edgerton and George Asche, they can guide you on cam and carb selection.
Langdons has an HEI for the small Mopar, I bet he can fix you up for the 265, or, you can build your own using a combo of GM HEI and Mopar parts
Not sure on the full pressure filtering, I have no filter on my race engine.
