That is an aftermarket addition that was used to bypass a clogged internal oil passageway in the block and/or the cylinder head. Either do a full disassembly and clear the clog, or use the bypass line to keep the top end oiled. At one time, Lisle, OTC, or one of the other specialty tool suppliers sold a precision fitted dowel that was inserted into the passenger's side center head bolt hole to clear the clog. Remove the head bolt, fill the hole with motor oil, insert the dowel, and smack it HARD with a BFH. The hydraulic pressure would clear the clogged passage- - - -sometimes!
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!