Assuming you are talking about the rear wheel If you can strip the rim you will find the inner and outer spokes on each side of the rim are the same length, considering the spoke nipple holes in the rim are drilled along the centre line of the rim and the flanges of the hub are also centre of the hub all you need to worry about is the flanges of the hub being symetrical to the rim,
The rear laverda hub has a bit of stuff hanging off the drive side so just worry about the hub flanges as your reference point.
Make your new spokes the same length and the rest will be easy. I may have some lengths if you are stuck
M.