@nvrenuf a single mount works well, like bp71 said, the second crossmember can work well as a support for a skid but isn't necessary for drivetrain support. I like the idea of a 2nd mount for bounce support since the motormounts and doubler adapter are so far apart but after treating our U4 car like a race car with only motormounts and the doubler adapter mounted and never breaking a TH350 case, I gotta say they hold up fine mounted that way. My K5 (ish) is the same way, we put a stock rubber 2wd 700R4 mount at the back of the trans and the main supports are welded to the Doubler adapter (Yup, it's still the one we built before TTC in 2001). The stock rubber t-case mount rotted away years ago and all that's left is the motor mounts and doubler adapter there too and the 700R4 case is still fine.
