I'm going to throw out a word of caution too.
It looks like the original used a solid coupling and a torque arm. The solid coupling is just that, a solid connection, so both ends should be tight with set set screw or two. The torque arm should be against something solid; like, the frame. The arm should be contained in a slot parallel to pump shaft to transfer torque and still allow some movement to relieve stress from pump shaft. So a solid coupling and flexible mount.
Your making a solid mount and a flexible coupling, which will also work, maybe better, as long as the solid mount is solid and the alignment can be maintained.
I think the original method was chosen because it will be difficult to make a good solid mount.
I'll be keen to see the outcome. Did the original pump fail? If so how did it fail, i.e leaking due to side load? Sometimes the connection between the torque arm and the retainer wears or something gets bent and puts stress on the pump shaft causing failure.
BTW, those chain couplings are way too expensive for me. I buy Love-Joyy equivalent for $20.00.
Yes to all Mr Nerd -
The chain setup protrudes a little further, but doesn't interfere with FEL, although it WILL be more exposed to being struck by debris. I don't anticipate a problem fabricating a robust bracket for the pump mount. I can weld some 1/4" plate bolt on and come out from the frame ends. I can also make a cover-cage to protect it above and below. Below are some photos of the original positioning.
I believe he was going to replace the original because the FEL and Backhoe moved slowly and he thought a bigger pump was needed. What he failed to do was flush the system, which was full of water and spooge. The new pump IS a good upgrade, but new hoses and cleaned out system will do wonders for operation.
I'm back to the original question: Which coupler is a better choice for this application.
Will the Lovejoy be a simpler, less failure prone solution?
Is the chain coupler hard to mount and align to the point it may cause pump failure?
I'm looking for the BEST setup. Since the pump and coupler were 'free' - I don't mind changing things.