The wagons used a different housing and lens for I believe both the brake and back-up lights than the cars. I know someone that had a collection of NOS 65' wagon related brake / back-up light related parts, PM if interested and I can get you in touch with them.
I agree, it is either an earlier tailgate or the mounting areas for both the back-up light recesses and trim have been filled in. If it is a 100 Series wagon I think it takes the way smaller and not often found tailgate diecast. But... saying that makes me think the 100 Series cars in 65' possibly did not have back-up lights so maybe the current setup is correct. It is also missing all the bright-work (cove moulding, drip rail, stainless around the window) which would be a further indication of a 100 Series, or someone removed the trim. Might be getting ahead of myself here though...