Painting over E-coat
 

I've got a repop core support I need to paint ... is there any problem with paint compatibility? I was planning on scuffing and painting with alkyd enamel. (oil base, similar to something like Rustoleum)

I painted a few parts that were e coated a few years back with rustoleum and had no issues. Has held up fine. I sprayed my e- coated core support with eastwood chassis black however as it's a bit more scratch resistant.

E Coat
 

You will need to see if it is soluble. Take a rag with lacquer thinner on it and try to rub off the E Coat. If it doesn’t come off, you’re good to go. If it does, you will need to remove it and proceed as you would with new metal to prevent potential future problems.
Some premium sealers do not require scuffing the E Coat, just a thorough cleaning. Doesn’t sound like you are going that direction so scuff away!

Thanks for the advice folks. I will proceed with the scuffing.