the "kits" that come with an oil psi gauge (clear or copper tubing/several brass fittings/adapter fittings) will let you put together an assembly with a 1/8 NPT male brass fitting at the end which is what you need to either go directly to the block or to a female reducer bushing. Those kits are sold seperately from gauges (& are cheap) so you might see about picking one up at your parts store as it sounds like you are missing a brass adapter fitting. Definitely no drilling/tapping needed. EDIT I'll see if I can get a pic later of the specific brass piece you need