Is it a single speed specific or track crank? As Tejanotrackie pointed out, that spindle length seems too long, unless it's a road crank being used as a single speed.

The Bottom bracket should be marked, but it is possible that it isn't, or that the markings have been destroyed.

This article is perfect for your needs. It explains the exact differences between JIS and ISO tapers. It also explains their potential interchangeability. You can mix-n-match, but the fit is different and therefore chain line will be affected. Sometimes a desired result can be achieved. Other times it throws things out of wack. The article has big clear color photos too, so identifying what you have should be doable.

https://www.sheldonbrown.com/bbtaper.html