Be careful because the 4/4 wire wheels have slightly more inset than Plus 4 and Roadster wires. The narrow bodied Plus 4 comes with 185/70 Avons, but clearance to the spring mount at the top of the crosshead is 2 or 3mm.
I tried 185/70 Blockleys but they fouled the spring mounting. So I think you should be Ok with a 175, but 185 is brand specific, so get the front clearance checked.
