I believe there where 2 radiators for the tb's in 85.
first half the year had the shorter ones like in the 84's, second part of 85's had the longer one that is the same length as the 86/87's (along with longer fan shroud). if its the second half, I'd go the fbody route as mentioned already as it would literally be a drop in replacement (no oil coolers on 85's).
if you have the shorter one, I'd hunt down the larger fan shroud and still do the fbody rad.
if you have the shorter one, they are the same as the rest of the NA regals and a replacement shouldnt be too hard.
call your local radiator shop. course those seem to be a dying breed these days