Re: Replacment of Lagoon ball valves
"Looking at that install though it would decrease my ID and restrict flow."
No, it shouldn't. The inside diameter of pipe stays the same whether it has straight or tapered threads on the outside. If your thru-hull fittings are NPS threads as they are in the USA, Then using the adapter to attach the NPT threaded ball valve will not reduce the flow.
The problem is we still don't know what threads you're thru-hulls have. If it's not NPS then the Groco Adapters or Seacocks will not work.
Retired from Hopkins-Carter Marine Supplies