Hi Steve .. I may be late to the party here, but here's what I find with the type of 'catalog' guitars you have there. More often than not, you don't need heat to release the extension. I check for runout, and then simply use my thinned spatula to work my way under. Just take your time, and work you way around. Usually a 2 minute or less operation. With that loose, I then wiggle the neck to see if it will come out dry. I once had a string of 8 guitars in a row where I needed no steam! I've found from experience that the hide glue used in many of these guitars was very brittle, or became brittle over time, and releases easily.
Another thing to watch, from my experience, is the relief of the neck/fingerboard. If excessive, you're guaranteed fret buzz at the 8th fret or so, after the neck set. I always assess/measure the relief and 'sponginess' of the neck (often made from poplar or basswood) before I begin the neck set. If excessive, I'll pull the fingerboard and inlay two carbon fiber rods, and then the neck is nice and flat; they're great players after that operation! Yes, I specialize in putting $800 worth of work into a $400 guitar
But it's satisfying.
Tom
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