Larry:
I'm not a 'Ferrari' guy and really not a 'Dino' guy, but I have done many an engine out etc on a lot of old cars. I'm along with you for the ride. Looks like fun to me. "a quarter-mile into my first around-the-block excursion, when the GT4 sputtered, stalled, and coasted to a stop." For a moment there I thought you were working on a Mopar. 🙂
Oh, that's not nice... I had somethgin similar happen to me on a test drive, when I had left a vise grip on the fuel line. I laughed out loud when I realized what I'd done.
I'm sure you've already spoken to, your friend, Marc Trahan, regarding the possible valve problem. That's one of those things where Ai'd talk to a few well versed people and see what they had to say. In the end, if the engine does fail, then it's just the right time for an LS swap! I had to throw that one in. 🙂