Anybody change from t12 to t8 ballasts..

I've done a ton of ballast replacements. If you already have 4' T-8 lamps, get these, or something similar:
GE 120-Volt Electronic Ballast for 4 ft. 2-Lamp T8 Fixture-GE232-120RESDIYB - The Home Depot

If you wanted 4' T-8 LED-replacement bulbs down the road, this electronic ballast should light them up. Otherwise use the commonly-available inexpensive T-8 bulbs, and just fix it. If you currently have 4' T-12 bulbs, these ballasts may not light them.

This is assuming you just want to repair the fixtures you have.

David V