Comments have been made about the Contra props and how they worked, it is correct they were needed to absorb the horses developed by the Griffon 58 but also needed to be able to transfer that power into the pulling of the of the Shack through the air, you may also notice the rear prop blades were a different profile and longer than the front prop blades, this was necessary due to supersonic tip speeds was discovered to be trying to bend the tips together thereby would have been quite problematic to flying under maximum power, ..I am not sure if the rear blades were made longer or the front blades shorter and fatter,
Also the Hybrid Mustang that was owned and flown by Gary Levitz at Reno, used Griffon 58's , that were fitted direct to the engine bearers with just a sliver of leather to act as a washer between the surfaces, the Contra prop sets were cut down rather crudely so that ground clearance would allow the take off and land back without fouling the runway, when I say crudely..it was done with a simple power hacksaw and finished with an angle grinder, it really is no wonder that the Mustang eventually broke up when going flat out killing Levitz in the process, I sold many used and zero timed Griffons to his aircraft builder in the early 90's along with all the various bits for the remaining Shack Griffon 58's ie Electric ignition systems and all the coils, plugs condensers, ECU's CSU's and all the prop spares, and many box's of new unused after refurbished props.
I did offer them around the UK but no one at the time had any interest, I had at one time many newly refurbed and fully cocooned Griffons in my warehouse, and many boxes of props, a visitor from the USA to my premises almost bought everything that would go into two 40 ft containers. before anyone try's to find me, I have nothing left.. except picture's!
Peter RB
Lancashire