I understand the clearances in the frame should be fine. Will the V-brakes still work?

depends on the length and adjustment of the v brake arms i think

unlikely 26 =559mm 700c =622mm there is over an inch increase in size to find so I dont think the v brake slot will be that long

I've seen it mentioned on here before with an on-one frame.

I'd like to retaint he V's, or even go for Canti's. I have mudguard mounts so suppose I could even go with calipers 😆

Is this a wind up?

Discs needed.

Mavic do a plate which effectively moves the canti bosses. SJS sell it, I'll see if I can find it. It's not cheap.

found it http://www.sjscycles.co.uk/product-Mavic-Mavic-Caliper-Adjusters–Each-12065.htm

you can get new braze ons for 50 quid

I converted a 26" frame to take 700c wheels last week using the Mavic caliper adjuster on the back and 700c forks on the front. V brakes do not have sufficient adjustment to 'reach' 700c rims. You could use the Mavic front and back but they are not particularly light and at £50 for the pair, not cheap either.

EDIT – Link to thread re Mavics