thumpism , curious what the BB on your frame is. As far as I can tell, '87 was the only year with the '3 main tubes 531' and solid, sparkly dark blue (red & black being the other option), so I assume ours are the same year. Mine has a Hatta BB, but it's got threaded studs that take a nut.....
Ah, but just now I'm thinking maybe yours is a 400D, while mine's a 400T, which might explain it...