Lower crank case ventilation hose

[johndemar]

A few weeks ago, my friend Russ, pointed out that my crank case hose was leaking. I figure no problem as it's just a matter of replacing the hose. The issue I've run into is that the replacement hose for a 76 appears to the same size coming out of the block and going into the cyclonic trap. The bib out of the block appears to be about 15.75mm and the trap about 19mm.
I know Fiat did some odd things when building these cars, but it appears I need the hose for the late 77-78 model. What is odd about this is that I have owned the car since new and the parts in question are original. Build date was 3/76 so it seems strange I would need the hose from a 78. Anyone else ever run into this?