/2 swingarm threads

[WooHoo]

I need some ideas on how to clean the female frame threads where the rear swingarm pivot bolts attach on a 55 /2 (Yes. I know it's not an airhead, nor a 'real' /2).

Mine came back from being resprayed with some paint in the threads, preventing the pivot bolts going in. I (mis)measured and bought a M20 x 1.5 tap but it's too wide across (the pivot bolt is 19.83mm wide).

Open to ideas.

Thanks

Tim