Defendant is indicted for a State Jail Felony drug case. in 1993, he was sentenced to two eight-year sentences for Indecency with a Child by Contact. Can I use one of the priors to make the drug case punished as a third degree pursuant to 12.35(c) and use the other prior to enhance the 12.35(c) state jail felony to a second degree felony pursuant to 12.42? Thanks.

I don't see why not. I would compare it to situations where courts have said you can use concurrent convictions to charge Felon in Possession of a Firearm and the other conviction to enhance to second degree.

It's not directly on point, but Cupit v. State out of Houston in '01 or '03 does a nice job of explaining enhancement options that are not specifically addressed in the statute.