Gear change changes.

Good to hear that all seems to work and making a difference. Obviously the fact that there were extra components available offered opportunities.
Assuming (always dangerous) that the bespoke stiffener continues to work satisfactorily do you think a “off the shelf” rigging turnbuckle would provide the necessary adjustment to get the lengths right and be a simple alternative?
Im not sure that the rose joints add a necessary advantage other than the ability to get the angles right during assembly.
The rigging screw might offer a cheaper ready made alternative.

I'm nearly as fond of turn buckles as I am of rose joints! I looked in my box where I keep them & found only items capable of tensioning rigging on a schooner. Had I embarked on the design of a system where the exact tensioning of one device against another was paramount, a turnbuckle would be the very device.
It would be incorrect to say that this design was poor, because it works, it would be correct to say there is scope for improvement & the greatest improvement would be at the bell housing anchor end. Had the engine been on the bench where I could have seen the relevant parts & measured accurately, I would have been able to give myself more pudding around the pipework & with an extra bend used only one rose joint.
I can see those improvements in my minds eye, which you may not be able to do, but had I done it the way I can imagine, what would I have used the remaining rose joint for?
M

If you read my thread about the clutch problem you will see that it raised its ugly head again last week. Today I made my version of the slave cylinder brace using 8mm rose joints that I also happened to have after a failed attempt at making drop links for the front anti roll bar. At the bellhousing end I used a piece of 40mm angle, nicely shaped with a flap wheel in the angle grinder. My slave cylinder end is totally different due to having 8mm joints, I simply unscrewed one of the mounting bolts and using a longer one just bolted it down with a nut between the joint and the slave cylinder foot. Like Airportable said, if you had the room to see to manufacture and fit it would be just an hours work.
I don't think that one of those  cheap turnbuckles will fit, they are simply too long. Looking back now I can see that I should have used the slave cylinder mounting bolt furthest from the bellhousing but even then the distance  between mounting bolt and bellhousing face is only 155mm. My mounting bracket at the bellhousing end effectively reduces that length by about 15mm