I am looking for more downhill speed control when loaded and was wondering if others may have installed an inline exhaust brake on a gasoline engine. In my case it would be on a 361.

 

Gasoline engines have a throttle that closes, resulting in the engine having to work against the closed throttle, creating high vacuum in the intake, as well as the compression in the cylinders, and friction and other loads imposed by accessories. That is your engine brake.

An exhaust plug on a gas engine, especially the 361, would simply give you burned valves, blown head gasket at worst, and no difference in engine retardation at best.

Downhill speed control starts at the top, being in the lowest gear and low range in the two speed rear axle, maintaining a low speed with the service brakes.

You should plan on going down the hill as slow as you went up it!

https://www.quora.com/Can-an-exhaust...-diesel-engine

 

It would help some on a gas engine but the benefit isn't worth the cost, the closed butterflies of the carb create a vacuum retarding effect, a closed exhaust would cause a pressure retarding on the exhaust stroke.
Because of the vacuum there would't be much exhaust to compress and with the gas engines low compression it would have little effect.
The FT/FE exhaust design doesn't offer a good tight sealing exhaust system needed for a exhaust brake
Lastly a standard gas engine can only handle around 10 psi of boost or exhaust back pressure where as a exhaust brake on a diesel will develop 40+ psi of back pressure.
On a gas engine 10 psi would have little braking effect and 40 psi would most likely push out the head gaskets.

Best to just gear down and take your time.