Sorry I'm late! I didn't know we were talking about piston conversions!! Ha. I still do a bunch of iron barrel 186cc tunes. I prefer not to shorten the cylinders these days, but its still a good option if you want to avoid the cost of a crank rebuild. That's definitely a 107 mazzuchelli rod rebuild, Wiseco Ts185 piston (they don't differentiate an ER type), and shortened barrel. Wiseco rings tend to be a larger gap than one might expect, so anything less than 0.020" out of the box is ok, although 0.010" is optimal.
The only way to measure bore clearance is with a proper bore gauge. I measure barrels for free (plus shipping of course) and check con rod/big end wear for free as well, but regardless, if you need a new piston, that's an older wiseco number. The new number is 176M06400. If you suspect you need a rebore, you could use a local bore/machine shop...then buy a 176M06450 and have them bore it to 0.0035", no less! Although for this one you also need to shorten the piston skirt. The generally accepted amount is to take 8mm from the skirt, although I think I've gone as little as 6.5mm to keep intake timing more reasonable (If I'm not doing it, tell them 7mm). I sell them for $110 standard, shortened I could do $125.
Also, that barrel isn't ported much, if at all. These can be great kits for short money if set up well. The head/combustion chamber should be checked too, to make sure it's not too high of a compression ratio...I've made that mistake myself in the past! It comes from recutting at too shallow of an angle and not opening up the chamber to compensate.