I have Crower roller rockers installed, and went to install a set of T&Ds last weekend, and the set came with a stand height gage tool that measures the top of the valve stem (when the valve is closed) relative to the rocker shaft.
It's fine if the valve stem is too high (needs shims) or if it is just right. But mine was too low, wherein the instructions recommended to "remove a corresponding amount of material from the stud bosses on the cylinder head:.
I'm not sure if that means removing the heads to get them machined, or if somehow the stud bosses on the heads can be shaved down with them still attached.
Either way it stopped my T&D RRs install dead cold, and I was
also uncertain if I needed longer rods for the installation as well.
So far I went back and reinstalled the Crowers, which have worked fine for around 3 years now.
If someone has some detailed info about this I'd gladly welcome it, but right now the T&D install doesn't fit as a "bolt-on" install, with a lack of detailed instructions for the non-professional, and possible machining work needed.