This is what I did for my link. If you look at the last picture I did not use the bell crank extension even though I have it.
I was never happy with height of my snow blade. I didn't know the difference at first and got a L-54 blade. I got most of the parts from TM Tom to make it a std 54A. Great quality parts but I just could not afford all of them so I had to reuse some of the old parts. I must have cut the bar fifteen times lengthening and shorting it. Today I went out and got some 3/4threaded and built a adjustable link.
The bar at the top is the one I was using for my top link
I found a heavy wall square steel tube That a 3/4 threaded rod fit into.
Bent a piece of flat stock into a U drilled a bolt hole in it and welded it to the pipe.
I ran two 3/4 nuts onto the rod and welded one to the pipe.
And cut one end off the old link and welded it to the threaded rod.
Now I can loosen the lock nut pull the top off the rock shaft screw
it in or out to set the blade where I want it.
This is it on the tractor. This is it on the Cub. It will work with the boomerang bar but I hooked it up like this so I would have more travel
so it would lift the blade higher.
I haven't even adjusted it yet and the blade lifts 7 inches. And I still have plenty of down pressure.