is contender frame #54xx a 1st yr production??

[tom ga hunter]

how do you change from rim to center fire??

[Geno]

Someone posted a link sometime back with "Estimated Manufacturing dates" which shows yours as Jan-June 1969. Second half of 1967 was first production year.  Change from rim to centerfire on the early un converted ones, I think, you had to turn the firing pin faceplate, something like that, I can't recall exactly, I think there's been a couple different hammers and selectors over the years. hope that helps some, otherwise one of these nice people will certainly assist.  

[Paladin]

there is a screw in the back of the hammer, with the hammer in safe position turn the screw 180* to change from centerfire to rimfire, or vise versa

good luck