It's a mess but good news as it can be quite difficult to get a dry oil pump to suck oil -- and, after 30+ years, your pump would have been very dry. Sounds like the oil filter was a little loose. The proper filter is very short. The same filter was used on many Renaults, just ask for one to suit a 1980 R5 with a 1.4 litre engine.
Again, good news about your engine's oil pressure!