another trivial thought: it's known that Masi would build frame with either Columbus or Reynolds 531 (customer's choice) and since there's no tubing decal this could be either (or even Falck tubing, but I'd doubt that).

Since the fork blades can't be 531 Imperial (wrong shape) I wonder if there are the Columbus-typical 5 spiral ridges in the steerer base...might not be a Columbus steerer, or too early to have those ridges but can't hurt to check.

If it's Reynolds, you might find the very small and faint stampings near the butt ends of the main tubes or on the steerer (have to remove the fork) but those are a long-shot and often can't be seen without magnification (or through paint).