Dennis, my old timing light (last used to set the timing on my F-100 and Maverick ) has no offset adjustment. However, I'd think it could still be used if one knew where the mark was supposed to be when the timing is set right. It may be off the scale, but it might be possible to fab something up for it to point to. 93 sounds like he's going to do the same test, so we shall see what his results are.
Most hot rod shops sell a self adhesive degree tape to fit around a balancer for crazy off the chart timing. If there's one big enough to fit around the balancer on these beasts, you could do it with your timing light.
-----Robert