Either the 6.6 or the 7.6 jugs should fit on your tractor. Assume you have the two piece valve boxes; a cast iron bottom with an aluminum top w/ door to adjust the valve lifter. Just get or assemble a jug with the upper plates under the valve springs and install on your engine.
If possible, I would use a 7.6 jug as its top flange is much heavier than the older 6.6 and it won't strip out the head bolt holes as easy or break off a corner of the flange (have one of those). Also, I used studs in the last one I assembled to more evenly load the CI head and head gasket.
Did want to try and machine and tap the exhaust port for a 1" NPT pipe to repair the broken flanges but not sure if the overheated iron will take a tap and cut the threads correctly. There was a thread on here somewhere about fixing ports, I just don't remember which one.
Good luck
If possible, I would use a 7.6 jug as its top flange is much heavier than the older 6.6 and it won't strip out the head bolt holes as easy or break off a corner of the flange (have one of those). Also, I used studs in the last one I assembled to more evenly load the CI head and head gasket.
Did want to try and machine and tap the exhaust port for a 1" NPT pipe to repair the broken flanges but not sure if the overheated iron will take a tap and cut the threads correctly. There was a thread on here somewhere about fixing ports, I just don't remember which one.
Good luck
