Blind guessing .. The fork blade length out of the box may only be so long, so radius of tire is limited..

I scored a Long round fork blade for my custom build , from the tandem frame producer supplying
Burly, in the 90's


IDK what the materials resources is for your builder .. You asking for Light weight , that may be the limitation..

I had A Cargo bike builder help me put together My Rock solid touring frame .

to some extent, I was Winging it on design features .. a hands on shop access process,
for the 2 of US.

My wheel 622-40..

Can't they work with an existing Suspension corrected, rigid Fork,? those have pretty long blades



Here is What? No build drawings offered above..