The problems with the front right driver frame were likely because of the way that #9 and similar Portland Forneys were designed from the get go. That is, the load of the train passed through the boiler to the cylinder saddle to the frame. This put a lot of stress on the entire boiler/smokebox/cylinder saddle/frame intersection. Add in the forces from the engine's movement over the track, and the piston thrust which tries to stretch the frame, and the result would appear to be that the two 3/4" bolts holding the frame parts together weren't sufficient and failed to keep things from working, or moving relative to each other in service.
My understanding is that this arrangement worked well enough on the smaller Forneys, but as the size moved up, problems surfaced, and the frames were designed to pass around the firebox so that the frame bore the train's load. We're implementing that design on #9's frame in this rebuild.
It looks like on the left side the lower frame member may have been replaced because the part that the bolts pass through is thicker than the right side piece and the joint was still tight. On the engineer's side, when we disassembled things the two bolts which held the lower frame member to the main frame were clearly worn. The holes through the front of the pedestal had been repaired with a threaded plug which was then re-drilled to the correct hole size for the two bolts, and there was also a 'U' shaped clamp which attempted to hold the lower piece up tight against the main frame.
We would like to replace the entire lower frame member, which is essentially a long 'T' shaped piece of 2" X 2" wrought iron. However, the long bolts which hold it and the main frame together with the cylinders are thoroughly rusted in place, and we fear removing them might damage the cylinder casting.
I don't know why the old mechanics didn't try a longer binder to catch that front frame piece. It seems to be an easy way of reinforcing the joint in the most effective direction, which is the direction of the piston thrust when it tries to stretch the frame. Otherwise we are trying to reduce the stress on the two bolts and increase the stiffness of the joint. There will be a plate on either side all bolted through with dry-fit bolts.
Here is a CAD drawing that shows this part of the main frame in grey, and the lower frame member in light green. The new binder and the reinforcing plates are in red. The cylinders are to your right. The bolts aren't shown but I hope you can get the gist of what I'm trying to describe.
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