Repeat, I should know the answer to this question: what thread size for the wheel lugs in a 69 bird? 1/2-20 maybe? Thank you people!

All B,E and C bodies from around 1958 and up use 1/2x20 SAE thread size. Some earlier years before 1968 used bolts instead of studs but I'm not sure when that stopped
A bodies from 1960 up to 1972 used 7/16x24 threads is what i remember, both sizes had left hand threads on the drivers sides and right hand on the passenger side

Cab has it right.
however, as there has been many, many, years gone by since these cars were new, it's a good idea to check if the studs have been converted to all right hand threads.
as to when the bolts were stopped being used, if i remember correctly [?], it was 1955.