how high will a 273 rev.

FWIW, Steve Dulcich wrote an article in the winter edition of Engine Masters on a 400hp+ build up of a 318. In the aformentioned article, Mr. Dulcich states that the 318 is good for 6500 rpm with stock rods, aftermarket rod bolts, stock valve train with the exception of aftermarket springs and a cast crank.

This is assuming that the valve train and all other clearances are set up correctly and this is not a tired old engine with 200,000 miles on the crank. Steve Dulcich has built more small block Mopars than I've even seen, so I would trust his judgement implicitly.

I have not personaly rapped a 273 up, but I have run a 360 Mopar, 302, 400M, and 351 Cleveland Fords up to 6000+ R's with stock rods, ARP rod bolts and cast cranks without any ill effects. But then again, I built these engines myself.