Wayno,
True the birdshead grip frames are all just one size no matter which model they come on.
It's true the birdsheads you have feel like a 2x4. I also call them plywood although the slaps laminated together all have the grain in the same direction. They are resin impregnated and as Caryc said, extremely easy to reshape and do not need refinishing, just ground down on a grinder or belt sander, sanded with progressively finer sand paper, and ending with 2000 grit. They'll look pretty good at that point but another two minutes on a power buffer will make them look like factory. They smell awful when you sand them but they can be worked down beautifully.
The standard plow handle grips, even Super BH grips cannot be fit to them. The rear bulge is too wide.