Simple question...are exhaust brakes hard on head gaskets or other downsides to them?

Eb are not hard on headgaskets assuming you are not injecting fuel when using one going down the road.  The eb is just creating a pumping loss in the engine.  

 

There is far less cylinder pressure being created compared to an actual power stroke of the engine

Nearly 270k miles on my head gasket with the use of an exhaust brake. They will apply around 60 PSI of drive pressure on the exhaust brake. There is no fuel applied during the exhaust braking so the pressure are much lower than say high timing and big injectors with high boost.

I have run mine for about 170k miles. The only problem I have had is the EB actuator blew. No problems on the engine.

And just to clarify, on vp trucks it's not necessary to upgrade valve spring like with the 12 valves? At least that's what I was told.

1 hour ago, Dieselfuture said:

And just to clarify, on vp trucks it's not necessary to upgrade valve spring like with the 12 valves? At least that's what I was told.

Correct. 12V motors came with weaker springs and have a larger surface area per valve. 

What exactly does the exhaust brake do? I realize the outcome. Lol. 

By blocking the exit of air from the engine you force the engine to compress pressurized air during hte exhaust stroke rather than allowing that air to exit . 

This creates a large pumping loose in the engine and then you have an engine brake.