The issue with using a tripod (I also have a mother of an old Manfrotto and do a lot of animal work as well) is that attaching any boom to that short 3/8" stud on top of the tripod would be a recipe for disaster.
A tripod top was designed for minimal/zero sideways load and a lot of (directly) downward load. For just a light sitting directly on top of the tripod (instead of say heavy camera), no boom, likely fine if ever a stand short.
But a nice baby pin, or better yet junior pin/socket stand that will take a weight cantilevered out from the base is what is needed for booms or 40" arms. As you know with horses, you spook them once because something wobbles, falls, shifts and it's shoot over - and that's the best case scenario.
I use C stands and 40" arms for smaller gear and large 'Mother' junior pin/socket wheeled stands and booms for heavier. Never aluminum risers, only steel - heavier, sturdier and will bend before (or instead of) breaking vs. alu (depending on quality) can often just fracture in a worst case scenario..
That, safety cables, sand (actually gravel, as sand too messy if leaks), boom/arm counterweights (takes rotational force off the grip head) - and as you note, weight over a leg.
You can NEVER over-engineer grip setups. Worst case of doing so is you lug too much gear, but it saves gym time ;> For lighter gear, the very portable all-steel Matthews Maxi Kit stand works like a charm.
