Another thing you could do is to find a drive shaft shop, most of these shops can make anything you want and will tell you how to measure for the shaft.
I was able to have a shaft made for my 1955 GMC and I had it balanced. The shop I went to did everything from large trucks to 4 x 4 they had blank yokes which could be machined for your needs.

Dave


1955 GMC Suburban Carrier
www.1955gmc.com