I'd stay away from running without 02s. No way to get closed-loop operation.. Likely impacts fuel economy under cruise (part throttle) conditions.
Modern high-flow cats shouldn't create much backpressure.
Couldn't resist not driving it after it would fire up
![Wink ;)](https://board.marlincrawler.com/Smileys/marlin/wink.gif)
clutch would slip. Nice power. Not meant to run without O2s and a cat.