They are different sizes, off the top of my head I think one is a 32mm and the other a 34mm diametre. Don't quote me on that, I don't have the standard calipers on my Wee any more so my memory of the stock ones is a bit flaky.
I thought all the non abs calipers were the same for v and wee. I ended up going direct to the dealer for mine. I'm pretty sure for my k7 both pistons and seals were identical up front.
Shows just how little I still know, even having done a caliper overhaul. Wish I'd just stumped up and let my mechanic do the work. Cost me a good 6 hours of my life trying to get them cleaned up and bled and they still weren't the best until I paid him half an hour to bleed them and grease them properly.
Would love to keep spare calipers for a quick change over midwinter but they just cost too much and frankly, there's plenty of evidence it would, in my case, be money poorly spent. I'm finding I quite like taking my bike to my mechanic every two months in the off season. I pay him for an hour used as he sees fit (£40), go for a coffee and come back to a much happier wee. It's a cop out but saves me time and I feel a lot more confident so it's worth the money. Mean while I pretty much just adjust pressure and deflection.