I have to say the move to lighted sidemarkers in 1970 was a less-than-optimal, almost dumb, design idea. Especially the fronts. To simply change a front sidemarker bulb, you had to unbolt the sidemarker assembly, unscrew the fragile plastic lens, and try to push-twist out the bulb from the recessed pigtail connector within the housing. More often than not, the old bulb fought you to stay inserted. Worse still, the pigtail was crimped inside the assembly. Then, you risked cracking the fragile mounting holes of the lens when you reinstalled it into the housing. Dumb, dumb, dumb.
All you should've needed to do is twist the pigtail connector out, pull it loose and swap the bulb, then twist-insert it back in. Nothing else would've needed to be disassembled and risk being cracked.