...not a good idea, the rear rings are made out of some degree of stainless steel, and so are the bolts. Replacing them by the black steel ones will cause corrosion in long therm, has other temp./expansion coefficients and so a possibillity the bolts got seized up in the holes, breaking off at removal......you don't want that. Stainless steel bolts are howerer everywere to obtain, not very rare so I wouldn't tamper with that! (Been there, my home built engines has all ss bolts where I tried others in the past.)

Good luck,
Gerald