the covers with holes are from newer engines that had tubes from them to the air cleaner and a solid cap on one for oil filling [no tube at the front] - there would have been no valve cover holes on an original 283, and there could have been an optional pcv valve from the factory - the road draft tube is replaced with a domed plug that has a fitting for the rubber hose to the pcv valve at the carb base [not actually into the carb, but into the manifold] - no problems with that configuration as long as you check/clean the pcv regularly .... you'll find info on the original style valve in sect.8 of the shop manual
re-reading your missive, I think you may not be aware there was originally a road draft tube at the back of the block behind the distributor, which is where the pcv ties into, NOT into a valve cover
Bill
