90q/4000q rear caliper compatability

[WAUFX at aol.com]

howdy doo--

my new-to-me 90q is, sadly, in need of rear calipers due to some frozen solid 
return springs for the e-brake cables. i have some good, working rear 4000q  
calipers which, according to the family album and thepartsbin.com, will fit 
provided my vin is not above 240000. however, mine is something like 242xxx. 
so, i ask, what *is* the difference? family album lists the difference like 
this: the part ## for a 4000q LR caliper and a 90q up to vin # 240000 is 
853615423, but the part ## for a LR caliper after vin ## 240000 is 853615423 
A or AX or V, all of the calipers listed just have that additional letter 
after the part number as the only difference. anyone know what's up with 
this? thanks.

Megan