It could well be, the hydraulic followers should be relativley quite in operation (for an engine of that age anyway).

It maybe that the lifters bores are worn which in turn is reducing the oil pressure to the followers. There are a few people on this site though have had problems with these lifters.

By using the solids however would eradicate the problem as they do not rely on oil pressure to "take up the slck" between the cam and the rocker (if the bores arnt severely worn anyway) What oil are you using??

If you wanted more power, you would need to modify the head a lot more, especially on a N/A engine

This is the head from the engine i mentioned



https://passionford.com/forum/pictur...&pictureid=786