Red line for a stock 170/

Mike,

If the engine is stock, I would guess 5500 is probably about right for you cam, and especially valvesprings. If you feel it peak at 5500, that's probably where it goes into valve float. Mopar used pretty light valvesprings on their low performance engines as sort of a rev limiter. The valves would float right past the point of peak power. This way the engine wouldn't want to rev high enough to hurt itself, making it somewhat idiot proof.

The best way to determine a reasonable redline (or in this case shift point) would be test and tune night at your local track. Make a couple passes shifting at 5000, a couple at 5500 etc... until it quits getting quicker.

If you plan a more aggressive cam down the road, I wouldn't change much until then. Just have fun with it as-is.

Also, go looking for a low gear set for your 904. Just about any mid 80's and later 904 variant (Dakota, Jeep) core transmission should have what you need. If you run 1/8 mile, this will be a big help.