I'm going to put a 350 block into my '67 El Camino. Not having the 283 it originally came with, my question is: Is it a big deal to put a period-correct intake manifold (with oil filler tube) onto any old late-model 350 block? I already have the plain "Chevrolet"-script valve covers, and I know all 350s after '68 had the oil filler on the valve covers. I just want a reliable driver, but I would like it to look correct under the hood whether the numbers match or not. Thanks in advance.

You need to assure ther crankcase ventilation systems are still operating. The filler pipe MAY have a PCV valve in it. Some did. If not, there's supposed to be one in the rear of the block where the road draft tube "used" to go. That provision is not there in a 350 block.

IMO, you would be better off instaling a PCV vale in one valve cover and a "breather cap" in the other. Some of the aftermarket valve covers make this easy and "purdy".

Jim