JMT stock jet sizes on the 18mm carbs are 98 main and 38 pilot...although this did vary some with the model of the bike. Vertical 175's that I've seen use the 98/38 sizes. Sloper 175's and CL175 used slightly different sizes.
I go up a jet size from stock even with no changes in the bike, as Honda tended to jet a bit lean on most of their bikes. Tough call on the filters...these bikes are extremely sensitive to changes in the intake system. The long rubber tubes on a stock bike that lead to the air box are actually part of a tuned intake system that's designed to increase mid range rpm power. Pod filters probably don't breath any better (but since OEM filters are getting scarce and expensive you don't have much of a choice). I'd go once size up on the main jet and see how it works. If it doesn't show any major problems then leave it at that. On a mostly stock 175 getting jetting right on the money isn't going to produce enough power to be noticable anyway.