Well, the 58 MEL that I assebled had a surprisingly correct geometrie especially in the valve train section. Shaft nmounted rockers such as w. the MEL, FE, Chrysler etc. are not a very convenient or precise system. They are mostly not adjustable and therefore highly dependent on how exact the cilynder heads were machined. Most importantly the correct rocker tip to valve stem geometry has to be maintained. You can read various tutorials about how this would have to look like. There might be some cam grinder's tech section somewhere either on the web or in a catalog. I'm sure you'll goggle it out somewhere. Some magazines use illustrations which are a great pointer. Many FEs that I have seen needed to get their valve train whiggled into a compromise position. An other factor to deal with is proper lifter pre load. A great upgrade is to use adjustable rocker arms such as the early FE rockers or modern roller rockers for the same engine (interchange).
As for your question, other than the above mentioned inconveniencies, I don't think the MEL, FE, shaft mounted rocker system is causing too much trouble on a stock or moderate engine. On a hot application you should think about installing rocker shaft end supports.
The blue colour on your rocker tips remind me at the blue spots that were on my NOS FE Le Mans rods. Maybe it's some kind of rust protection to amke the product longer storable.
