Hi Ryan,
I'll have to say you've caught it early and thus it's easily repairable by a competent welder that won't need to spend hours on it.
As it's just a small section all you'll need to do is grind out a small channel along the fracture and then carefully weld it up. Honestly a welding tradesman will know exactly what he needs to do with a Mig welder and not induce twist into the chassis. Ensure that the roller and Bed knife are still installed while the repairs are being done. This will hold the frame rather rigid.
The key steel you have there will just require rubbing the high ridges off of it on a flat piece of emery paper.
Now here comes the sad part, purchasing the new clutch half that will set you back around $80 odd $$$$. The new style will have two pinning set screws that will pin the clutch body to the PTO shaft at right angles and thus it never should come loose like the old cotter pin clutches do. BTW it's the old clutch that's induced the fractures into the engine rail by running unbalanced.
I would also use a strip of emery and run it up and down the PTO shaft taking particular attention to the flared out key area as the edges will wear hnto high spots making it hard to install the new clutch body.
I'd say your clutch cork is still ok as it has plenty of thickness after you clean out the gunk around the edge of the cork.
Now I guess I should ask the obvious question, what are your long term intentions for the Model 45 ?
Cheers,
BB.
