Welding cast iron is a specialists job and believe me you're not the first to Pioneer this act so don't feel too bad. Model 33 clutches can be replaced with a Model 45 set up as the 33's are not available anywhere. Matter of fact Model 45 units are currently not available either as there has been a manufacturing issue with the bore size being out of whack as they come out of a mould and are not bored to size. All the current clutch halves out there are faulty and anyone thinking of purchasing one needs to be totally aware of the suspect units that are as bad as an old flogged out one. The nominal bore size should be 15.87mm, but these current units can be anywhere between 16mm and 16.5 and also slightly oval as well ranging between the two figures quoted above.
This observation is current at 20/06/2019 and will change at a later date, thus why I've documented the date here so when this is viewed in the future it'll probably no longer be relevant.
At this point in time the only way out is if you are buying a new engine is to buy a 3/4 sized PTO output shaft unit and then the respective clutch half to suit as those are originally made in 5/8 size and then bored out to 3/4 and as such are no issue at all.
Anyway in regards to your issue Hermosil, I'd wait until new 5/8 clutch halves are again of a satisfactory standard and then convert over to the 45 Model set up.
Cheers,
BB.
