Portage is a touring bike isn't it? Not a mountain bike. If it is a touring bike, then that to me means you likely have a 1.37" x 24 tpi english threaded (BSA) bb shell and probably just 68 mm wide. But you can measure that width and know for sure. I was starting to worry though as I remembered after my first post a lot of mountain bikes then were one piece cranks.

https://www.parktool.com/blog/repair...nd-terminology

If you want to put a cartridge bb in it, you'll need to know the current length of your spindle end to end. I'd also bet it is JIS tapered. But if you want to get a modern two piece crank, I'm sure that would fit too and you can have external cups to get a wider bearing spacing.