Find some cheap tires and rims to mock it up. Worn out tires are cheap.
Before you final weld that m II in place hang a fender on with a tire/rim mounted and step back to see how centered the wheel/tire are in the opening. Sometimes lowering the front will make the wheel/tire look like it’s tucked back towards the fender.
If you want to compare tire sizes just search on tire rack for 215 70 15, find a tire and look at the sizes chart. The chart will show different heights, widths, recommended rim width. All good info for tire selection.
https://www.tirerack.com/content/tir.../homepage.html
Is your 350 totally stock or a modified motor?