I'd definitely change the thermostat, just so you can rule it out. It's not hard to get to or expensive to replace.

The cooling fan shouldn't make much of a difference, because water isn't flowing through the radiator yet, if the thermostat is working.

The coated exhaust manifold shouldn't make much difference either, unless your 66 sedan has an integrated manifold. The integrated manifolds do noticeably warm up faster and are more friendly before being fully warmed up usually. Now, if you had an integrated manifold on the wagon, and had that coated inside and out, you'd probably notice a longer warm up than you're used to as well.

Also, is your engine sucking in air from the engine bay, or do you have a cold air setup? That would also slightly increase the warm up time, further increased by the coated exhaust manifold not heating up the engine bay as much.
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Kyle - 244! - Kawasaki Ninja 250R - Oregon Volvo Tuners?