dddd

I'll chime in, since I have measured hundreds of spindle tapers for comparative purposes.

Squirtdad's first post is solid info in my opinion.

These Ofmega spindle tapers are fairly close to ISO tapers, just a tiny bit smaller, so can be substituted imo.
Just as pre-cartridge Campagnolo spindles are pretty close to ISO dimensions. And, as onespeedbiker mentioned, the pre-cartridge Campag spindle tapers are a bit bigger than ISO tapers yet a good bit smaller than JIS to the tune of about 2mm in spindle/crankarm overlap.

I personally would try a 115mm symmetric JIS cartridge, as the missing "spindle offset" and thicker JIS taper should cancel each other out.
The new cartridge will act like a 120mm spindle but with a bit less offset, making the pedal stance more symmetrical in the process.
A splined tool will be needed to seat the cartridge's cups, but these cartridges can go without maintenance for many years in my experience.
Any deficiency in the "chainline" measurement of the seated right crankarm can be easily dealt with using a fixed cup spacer of perhaps 1-3mm, but you only need a millimeter or two of clearance between the small chainring and the right chainstay and there is probably already much more than that now.