Bravo steering arm issue

I'm in the process of putting my Bravo transom assembly back together on my bench. I installed a new stainless swivel pin and upon tightening the bolt on the steering arm, I noticed it had some side to side play. The arm can also move up and down on the pin. The arm has no signs of wear, and I can't make the bolt any tighter before it snaps! I think it just comes down to a bad design. The bolt doesn't really provide much clamping force at it's location due to the way the arm is designed. I'm not sure cast iron has much give before it breaks either. I thought of cutting a relief slit all the way thru at the back of the arm with a cutoff wheel. I don't know how much this will compromise the strength of the arm? failure at sea is not an option! Does anyone know of a solution to this problem?
Thanks. Cap.

Yes, A new transom Assembly. Mag assembly is around $2800.

By the time you are done putting yours together you will be spending more than half the price of a new one.

Yeah, well I won't dispute your logic, but with all the time I put into it already doing my own blasting and painting, my time was the larger expense. I think I'll pass on a new unit at this point and just figure out a way to improve on someones crappy design!

remove the arm ., flat file the surface, install in vise, heat and tighten pinch bolt untill it doesent fit the new pin.
Let cool ,remove pinch bolt and flat file to the exact size.

I wasn't fully convinced Mercury would continue to use the same essential part if it didn't work. I locked the steering arm in my vise
and oiled the threads. I also put a thin washer behind the nut. It took about 45 ft lbs and the arm clamped tight on the pin. I stand corrected!
I just need to lock the bolt down tighter. I doubt 45 lbs would break that bolt! Thanks for the input, Doc.