newark st. M-85 has fatter body, so that case may require some mods. should be do-able, but i modded a starfire bass case...because at that point of my efforts now i have a case that fits 2 different Guild basses...and to get technical actually I used an Epiphone Jack Cassady bass (also fits Starfire bass perfectly) case, so this case is good for *three different basses, should I ever need the options (or find a true M-85 case)
i want to say the body depth on the Starfire bass is much, much closer to the GSR M-85 than a Newark Street M85 body depth to GSR M85 body depth would be...mod is reversible as eluded to above.
the Epi Cassady case is a little bigger than the SF bass case, but not by much at all, so i went for the most versatility.
when shopping for cases for Guilds, consider Epiphone but stay away from Gibson! headstock areas are different, many Gibson cases are too small. (and if anyone needs a Gibson EB/SG bass case, hit me up!!)