I've been wondering about making some little extenders to bring up the bottom bracket height for a theoretical old-british-folding-bike build I'm considering (which potentially involves switching out 440 or 451 rims for 406 rims for the sake of tire availability).

Why?
Particularly am thinking about a Dawes Kingpin - these came stock with now-almost-impossible-to-find-tires-for 440 rims. They can fit 451 which have an OK but limited selection of tires, 406 rims are OK but the bottom bracket height starts to get quite low and puts you in frequent-pedal-strike territory (a friend measured theirs with 2" bmx tires on a 406 rim and had ~242mm bottom bracket height). Raleigh twenties bottom bracket heights (according to other friend's measurements) are about 20-25mm higher with similar rims/tires so probably are out of the danger zone for the most part.

Some assumptions I have/things I already know:

• Buying a different fork with a longer axle-to-crown would be a more elegant and easier solution, I might very well do that, but that probably involves buying new or getting lucky finding another cheap folder or very unusually-shaped recumbent to scavenge a fork from so probably is going to be relatively expensive compared to a couple small laser-cut parts.
• Buying a totally different folder with a geometry actually designed for 406 wheels would be cheaper and a better idea. True but I'm currently having fun imagining a wacky vintage build. If the right bike floats my way I will probably buy it and never do anything described below.
• This might put the rim outside of the range of even long-reach calipers and necessitate a drop bolt or cantilever posts to be added, I'm fine with that.
• The design described would increase the fork spacing, but most of the bikes in question already have a narrower-than-usual fork spacing, that's fine, it'd probably just bring it closer to a normal spacing and then I'd cold-set it to a standard spacing
• I'd need to also raise up the rear with either a modified dropout or a similar dropout adapter bolted into the existing slot. That seems relatively straightforward either way since the rear-end geometry seems less critical to handling (if anything maybe I could also stretch out the wheelbase a little)
• The forks in question have pressed dropouts (i.e. the fork blade tube is crimped down and a u-shaped dropout is stamped out of it).

My basic idea is to design a small plate that can be bolted onto the fork dropout which effectively creates a new dropout a little bit lower. It could also be welded/brazed on but right now I'm thinking a non-destructive mod might be preferable at least for experimentation. Probably the total lift would be in the range of 20-30mm.

Questions:

• Is this going to be a deathtrap? I imagine if I make these out of sufficiently thick stainless or 4130 they'd be plenty tough and have a hard time imagining how they'd fail other than bolts working themselves loose.
• Would designing the shape of the extension to preserve the trail of the fork (option A) result in similar handling? Are there other factors I'm unaware of?
• Are there any similar mods/products like this out there? I did some searching around to try and find anything but didn't turn up with much.

Please note that this doodle is in no way to scale and is just intended to illustrate the idea.