Staton sells regular old square taper crank arms that are the same as the ones I'm using. The problem is that there is no dish to the smallest sprocket. A flat sprocket only allows you to get the sprocket butted up to the adapters flange and not over hang the flang with a dish. Most front sprocket sets have a dish for this very reason.
My bottom bracket is 2.630" inches wide and with the 27 tooth ring almost butted to the right side bottom bracket bearing carrier the front chainring gears are almost perfectly centered with the rear 7 speed cluster casset. Guess I was lucky.
Do you have any spare room between your most outboard gear on the rear casset and the frame tube/dropout? If so, you could spacer the the rear casset more in the outboard direction to get better alignment.
My philosophy is to look at these motorbike kits as "universal" kits made to work on all different types, styles, and variaty of bikes.............not everything is going to fit up perfectly because of the "universal" nature and some adjusting, tweaking, cutting, and fitting is going to be necessary for different bike types. ............Don