Either one will put meat in the freezer for another century.
Sights on the Number 4 are better, especially if you like peep sights.
PARTS for the Number 4 are slightly easier to get IF you ever need them.
Extractor springs, mag release springs and sear springs interchange; these are the most common parts to weaken or break.
As to THREADS, neither one interchanges with ANYTHING you are likely to run into. Number 1 uses Enfield threads, Number 4 uses BA threads. BA threads are a PITA but at least you can get them from a model engineering shop. For Enfield threads, you are pretty much limited to take-offs unless you are lucky enough to find a few new ones.
Either rifle is slightly more reliable than a brick: they rarely ever break down.
BTW, you will get best accuracy with either rifle by sticking to .312" slugs.
Hope this helps.