I haven't got a spec for this. I built it as I went along using 60x40 box section grafted onto the goldwings swingarm.
As for how much I reduced it by. I'm not 100% sure as I lined the centre of differential up whit the bikes output shaft. then from the centre of the bike I measured to the axle back plates and cut off the difference.
I cant even take measurements for you now as I have just sold this trike
This is the place to show off your photos / details of your own trike build or resoration profect.