Seller says it can be used for 26'' to 700C conversion.
What he doesn't say is that you are literally doubling the pivot to pad distance while keeping the original pivot to cable stop distance. Switching to road levers might get back enough mechanical advantage to make it work tolerably.
There are brakes on ebay. Seller says it can be used for 26'' to 700C conversion.
https://www.ebay.com/itm/Taiwan-made-Patent-Alloy-V-Brake-For-20-406-451-26-and-700C-Rim-Red/130659020833?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20131231084308%26meid%3D9e8b948c950848b18b66548e184dd4db%26pid%3D100010%26rk%3D2%26rkt%3D4%26sd%3D251282115326%26itm%3D130659020833&_trksid=p2047675.c100010.m2109