Brakes brakes baby

Sooooooo, I’m building a Soma Buena Vista for my wife.
Soma says you can run 650B wheels with extra lng reach brakes.
Bought a set of Tektro R559s - no dice. About 2-3mm short.

Any suggestions? Anyone had experience with these frames?

File 'em?

Dia compe 750 centrepulls.

2mm more reach than r559.

Or bdop drop pad holders.

Or gigantex holders

So do Dia Compe 750s work ok?

Bdop holders look ok.

Or just go 700C wheels, smaller tyres & a Soma front rack I guess.

Anyone got any of those pad holders locally that they wanna offload? or know of anywhere to buy locally?