Obryn
Hero
I'll note that, by my reading, "Convert" means "Open your 1e PHB and use as-is."1) Certain creatures are WOTC's IP and not included in the OGL, SRD, or Tome of Horrors--those would need to be converted to an OSRIC equivalent.
2) There are no psionics in OSRIC, which would be an issue for one or two modules where creatures would need to be given magical powers instead of psionic ones. This doesn't apply to very many of them.
3) Monks or bards would need to be converted. This applies to one or two modules at most, since they were fairly rare in original 1e products.

-O