Welcome here!
on barrel fitting i would guess the faqs are probably correct.
but you could call customer service and ask.
all the factory buttstocks i believe interchange. some fore ends can be a little more work, different barrel channel size.
if the .243 locks up tight and solid and shoots fine, whats the worry?
congratulations on the hornet, everyone that has one likes it!
I just got a .243 barrel for mine and am looking forward to trying it out.