I'm not familiar with the GMC engines, but I have seen it done on 235's. It actually makes alot of sense to feed your rocker arms vs. just dumping it back in the pan.
In the case of the 235, you would need to block off the internal oil feed, otherwise you would be getting too much oil to the top end.
You still may even get too much to the top end, so you may have to put an orifice inline to help control the amount of oil flow.
