[55 Chevy]

The very early 283 (57), with the part number 3731548(as did the 3720991 265's) had a notch in the rear cam journal surface to basically link the block oil galleys at the # 5, the far back one feeding the rockers. It used a thinner cam plug at the back to not block that hole and if the newer style plug was used it would. Thus no oil up top. The trick was to either grind a feed hole in the block at the rear cam journal linking the two oil feed holes. Or oblong the hole in the # 5 cam bearing to link the two.

Not sure if this is the case with your 283 but just a thought. I don't know when GM made the change in the blocks,I believe it was the late fifties but i really don't know. These blocks also had no provisions for side mounts which your '63 would need.

If you did just a straight camshaft and lifter swap and not changed the rear cam plug when things worked before,this is not the problem. But just a thought.

Also on the very early 55-57 small blocks, if you used a newer style distributor instead of the original with a notch at the bottom that distributor would fill with oil as it could not drain back through the block. So mods were needed there too.