Since the downstream (rocker arm) side of the oil distributor has a check valve in it that only opens when the pressure to the main bearings is above 15 PSI, a restrictor isn't really necessary. Very few 216's have that much oil pressure below highway cruising speed, so the oil supply to the rocker arms is going to be intermittent at best, with or without a restrictor. If you think you really need one, drill and tap the fitting for a carburetor main jet. I have a few dozen Holley jets left over from my round track racing days that I use for that type of restrictor.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!