Dale--
I don't think any race group specifies how and from what material the hoop is to be made. For example, Vintage Racer Group's says: "3.2.6.6. Drive shaft: It is recommended that all front-engine, rear-wheel-drive cars have a 360o safety hoop enclosing the drive shaft, to protect the driver in the event of u-joint failure."
If a car's driveshaft has two yokes--as does that in an Austin-Healey--then since either U joint can fail you really would want two hoops as one in the middle might not capture a flailing driveshaft. If a driveshaft connects to the transmission via a sliding yoke--as is the case with the MG transmissions in both the Elvas and the Ford transmission in the Ginetta--one needs only to be concerned with containing it where it couples to the differential.
Below are pictures showing the hoops I fashioned out of steel strapping for the Courier and the box sections that are parts of the Ginetta's construction. Notwithstanding my statement in the preceding paragraph, in the Courier I put in two hoops with U-shaped strapping above the driveshaft and flat strapping below, all bolted into angles welded up to the fore and aft frame rails, the front one serving to make the sheet metal tunnel stiffer and that is the one pictured. The rear hoop is much the same and captures the driveshaft at the rear cockpit bulkhead, close to its point of attachment to the differential flange. Both setups provide 360o protection.
Whether you choose to entirely surround the driveshaft 360 degrees or simply have a hoop that goes over the shaft, laminating it into the FG transmission tunnel sounds like an unnecessary complication and, depending upon attachment points in the longitudinal frame members, might make it very difficult if not impossible to pull the tunnel without removing both seats and other interior panels. Rather, I would suggest that you fashion hoops that would fit under and close to the tunnel as I did with the Courier and depending upon how you do things this might make installing/removing the tunnel easier.