I'm lost here lol, so the hyd flats are taller than hughes roller? How many miles you have so far? How are you running a mag cam? You have an electric fuel pump?
The rollers are taller, which pulls the bottom of the pushrod down towards the cylinders. The flat tappet lifters push the bottom of the pushrod away from the cylinder which made the pushrod contact the intake side of the pushrod passage in the cylinder head.
I don't have many miles yet. Put the motor back together last winter at a buddies shop and drove it home a couple of months ago. Since then I have been fixing other things and waiting for the weather to improve, so all I've done is drive it around town. Maybe 75 or 100 miles is all.
I bought a cam snout extension from Hughes so I can run a fuel pump eccentric. No electric pump right now.
Only problem I have right now is I think the pushrods are a bit long, about .080" preload. Talked to Hughes about it and they said it was about right, but I don't know. I think I will probably get some shorter ones at some point in time.