-
Cheapest solution is to simply carry on with what you're doing, having said that, you won't regret it since it'll be very comfortable, less likely to cause a lots of vibration on the front rack, and easy to just go on a straight line and not worry about potholes.
The 650b conversion is reversible anyway, so it can be changed in future if you want to extend the bike's usability further.
Thanks for all the info. Realistically I know the bike will just be ridden around town in good weather, so maybe not worth the 650b mods - but then will I regret it afterwards being the tart I am? One to think about, or potentially going full Frenchie as a stage 2.