A stock Caddy thermostat has a bell shape deal on the bottom of it. That bell covers the bypass that Caddy installed to warm the motor quickly. You can tap and plug this hole so that a standard Chevy type thermostat can be used, or none at all if you choose. You will need a 1" plug and tap the hole under the thermostat housing with a standard pipe tap. Drill a small, 1/8" or so, hole in the plug so that it won't air lock.
What type of mods are you allowed in this class? A dual plane intake off a 472/500 flows better than a 425s single plane. A ported 472/500 intake will come close to a stock Edelbrock as far as power and flow. A 1" carb spacer will do wonders as well. Your heads have 2" intake, and 1.625 exhaust valves stock. You can use Pontiac valves in your Cad heads for a cheap upgrade. A 2.11" valve will flow much more than a 2". You should shoot for 32* total in the timing department. Fuel pump flow is also a real issue with the Cad. They can't hardly keep up with a stock motor, let alone under racing conditions. You can use a high flow Olds pump by changing the arm out for the Caddy piece. A 472 or 500 will also bolt in place of the 425. Being a Cadillac, nobody would know anyway......Dan
One other thing. Have you had the car across the scales yet? They aren't as heavy as everybody thinks........