Dave, don't worry about it too much. I would of mounted the crade solid and put only the bushings between the cradle and the adaptor. However, the more bushings you have in there, the more the load is spread out, so you basically have two different connections with 4 bushings each right? So each bushing has 1/4 the load if you only had one bushing each. I really don't think you'll have much of an issue with drivetrain movement. As long as you have a crossmember close enough to your front cradle mounts, to keep the frame from twisting or pulling in there.
I only have 4 bushings holding the main forces of my front axle (front/rear load, pinion defelection, braking twist, etc), and it is working fine even with 8.2:1 gear reduction in the torque.
The factory only has 2 bushings holding the engine torque, and one or two holding the trans/tcase weight. You have twice that many holding your doubler, and it's probably not much heaver than an NP203.
So my guess is it will be fine. But if not, just put some delrin or aluminum bushings in the frame to cradle mounts.