M1 Carbine question

sorry for posting here...but i didnt see a Carbine forum.

i have a Winchester M1 carbine..serial #5561XXX.

it is a Blue Sky import. averaging 6inch groups @ 100meters.
the rifling and crown are gone. just ordered a new barrel from Tapco for $99.

i noticed while shooting..the iron site has a tendency to jump back from 100 to 150. i am considering ordering/installing a new rear site instead of trying to fix it.

my question is. did this Winchester orginally have a Flip up site or an adjustable A2 site? my receiver has no date of MFG that i can see.

thanks in advance.