I took the Jet Gun in to a hydraulic shop for fittings and also a new hose (huge kudos to Rodney at CanLand Hydraulics in Belleville ON- superb customer service and product knowledge). Quick-connect S/S fittings and hose good for 3,000lbs.
Another local outfit in Belleville welds polyethylene, so the tank repair should be ready in a few weeks.
But, I could not resist a trial. Lubed it thoroughly, took off the two "Pump Caps" (pump cases- missing one O-ring but mirror-shiny piston bores), turned it over by hand then re-assembled, bolted it to the 5665 and filled the tank.
Well, well, well! After spitting out a couple of pints of rusty water through the hose, it then gathered steam and started spraying up to 20 feet with the gun. A pleasant surprise.
It was puking water from every orifice: I'm going to have to get both a new strainer threaded plug and also figure out how to replace the front seal along with the tank repair. A lick of paint and s/s fasteners, and it will be showroom-floor condition
Built when Gravely was the Standard of the World.
/if any MTF Gravely guy would have a MA 709 Operator's Manual, I'd be greatly obliged for a .pdf.