I've used the G2 caliper paint. Worked well enough. Powder coating would be ideal. I imagine they have some method of protecting the piston bores and blocking the holes.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.