There are essentially four components to the project: the 106mm gun itself, the semiauto M8C .50 caliber spotting rifle mounted above the 106mm barrel and used to zero in on the target, [and a fun little item in itself] the M79 mount or any of a couple of other possibilities, though the wheeled M79 is more practical than most, allowing fairly quick and easy removal and installation of the unit in and out of the vehicle, and of course the mounting vehicle itself, anything from the six-gun tracked *Ontos* used by the USMC as a light tank destroyer and bunker buster to the more usual jeep and other light truck platforms, which require some rear suspension modifications to handle the additional weight and a folddown, removable or split windshield to accomodate the gun tube when mounted. The U.S. M151 series jeep, known as the M151A1C when set up as a recoilless mount, is probably the most common, but several earlier and later Jeeps and light trucks are possible, particularly those nneat Brit and Aussie Land Rovers.
My own suggestion is to begin with the vehicle, and add a dummy or display gun, maybe fitted with one of the subcaliber gunnery practice units for initial familiarization, then upgrading your equipment as the better components come along. There's a fellow who specializes in M40A1/M40A2 restoration work, and I'd be glad to point you to him; my own next project is a 20mm subcaliber unit, chambered for the same 20x139b mm ammunition as the Lahti and Solothurn *light* antitank rifles of the early WWII period, which render the gun not-quite recoilless any longer, but the weight and bulk of the M40A1 can handle it okay- some are considering a similar setup for the 25x137 mm main gun of the M2 Bradley mech infantry vehicle.
Main gun ammunition is difficult to come by but dummy solid shot practice rounds are easily available ($35-$50 apiece; the jeep-mounted guns carried six shots aboard, with more sometimes carried in a trailer or companion vehicle) and there's a fella in Texas with load development info he worked up for his own 57mm M18A1 recoilless- it's a starting place, at least.
They're not something you shoot just anywhere or anytime, but they do provide a good deal of interest when you do. And they're great sport for 4th of July and Memorial Day/Veterans' Day parades.
-archy-/-
