My last go around was with Manton and I'm very please with their service. One thing you should consider if you are building/engineering the engine is restricting oiling upstairs via the pushrods. When I mapped-out the single shaft geo on my single shaft TD system I had sleeves with the .750 hole offset +vertically with 'bush-up' to the OEM stand diameter which is .875"? ish which helped geometry. Know too that there was IIRC about .015" more lift at the valve if you used the longest acceptable pushrod.