Aires Hobby Models has come out with an excellent upgrade for the Trumpeter MiG-23 MF / ML kits with their Correct Air Intakes set. There are six parts cast in a durable resin material along with four resin clear parts. The Aires parts provide improved air intake detail. The instructions show where the additional parts go and then its simply a swap out for the Trumpeter intakes.
Aires has molded the air intakes perfectly in tan resin with no apparent bubbles. The Aires air intakes are supplied on a four resin sprue with thin resin attachments to the parts that should minimize any cleanup.
Although most paints will adhere to resin alone, I would recommend that washing the parts to remove any remaining mold release and prime them first. They will need to be installed with your favorite CA (super glue) or epoxy, as the normal plastic glues or solvents will not react with the resin.