[Gaz64]

One issue with this shaft mount design is it only has 4 mounting points.
Each pair of valve springs pushes against only 1 stud.

Conversely, some designs have 5 mounting points, bolts or studs.

5 in total gives 2 studs for each pair of valves to push against.

I would timesert or helicoil all the mounting points to run the largest stud possible in the head, even meaning a stepped stud.

The stud should be loctited, and just nipped into the head before the rockers are fitted.

I would also leakdown test all cylinders while the rockers are off to find any leaking valves.

Gary