Dave,I sent a note to a retired friend who might assist, but even there,his experience ( he and I joined SA about the same time) might begin after the T-58/S-61 engine/airframe interface issues were designed and tested. I’d suggest you get in touch with both Westland Engr Dept and Rolls and see if they can connect you with some of their retirees who may recall the details you are looking for. I dimly remember conversations about early T-58 high speed shaft issues,but that’s about it.