The mud motors weather be SD or LT have the same concept; to get you through the devils playgrounds of mud, stumps, weeds, and slop.....

I've noticed that there are 3 main power plants for the Mud Motors.

Honda

Vanguard

Briggs & Stratton

Based on motor only (not the design of the mud motor as a whole) is there any true performance, maintenance, and reliablity difference between them?

Oh $hit here we go

In your hours of research you forgot to add Kohler.

They are all good. Just run what makes you feel comfortable or is available on the mud motor brand of your choice. Personally, I wouldn't let the engine brand stop me from buying one MM or another.