I've used a bunch of different single shaft aluminum roller rocker arm set up's including T&D and Harland Sharps. I've seen a small variance in the net lift on both the H.S. and T&D, I prefer the H.S. as they will custom make the exact ratio you want if your willing to wait a week or two
I just finish dealing with a issue on a set of T&D single shaft that where suppose to be 1.65 ratio that ended up being 1.76 or so on a set of 440-1 heads That really messes with the coil bind when setting up the valve springs based on net lift
Luckily I ended up checking the net lift at the retainer and discover that issue before delivering the motor to my customer, it was a pain in the butt to fix it on the engine also
I will buy H.S. before I buy another set of T&D single shaft sytem