Is it posible to retro fit the older tail lights (1970 or so) onto an 85?

depends on your body man. the openings in the body are different, but the overall shape is the same. So yes it can be done, but you need to weld in some steel and make new openings for the smaller lights. i like the 68 style lights myself

not without some body modifications. Unfortunately, it means adding metal and not subtracting. There is a difference in early lights as well, so left and right need to be of the same year.

azruss wrote:not without some body modifications. Unfortunately, it means adding metal and not subtracting. There is a difference in early lights as well, so left and right need to be of the same year.

'It appears at some point the tail light opening increased in size. Anyone know what year that was?

1979

There are 4 spider tail lights.

'66-69 ... Single lens assembly w/o provision for reverse lens. The smallest assembly
~1971 (generally 1608cc cars)... Single turn signal & brake lens with separate reverse lens... The longest assembly
1970 and-1972-78... Separate turn signal, brake and reverse lens
1979on ... Teardrop style assembly ... Overall the largest assembly

It would take a bit of work to make any of the early assemblies fit in a late model Spider