I would still check the intake bolts, when the engine is hot. For all you know, you could have some loose ones. You don't need or want to horse them down, just get em good and snug. Although there's a torque spec to follow, it's difficult to get a clear shot with a torque wrench on at least half the bolts. Don't worry, you're not going to crush the gasket either.
And yeah, checking for a vacuum leak with starting fluid is a good way to do it. Some guys have suggested using carb cleaner, but since that stuff loosens paint, I wouldn't.
One more thing, make sure the choke is opening up all the way.

 

I'm going to run through the intake bolts and try the starter fluid test. I've talked with two mechanic fiends over the phone tonight and they've both recommended I check out the condenser. The feeling is that if the intake was leaking, it would do so when the engine was cold and not when it was heated up and the metal swollen. Unfortunately, I couldn't get an answer out of them as to why the condenser would be a problem only after 45-60 minutes of drive time. Needless to say, I have a lot of things to check tomorrow and thankfully, most of it I can do here.

 

This exact thing (almost) was happening with my nephews 69. It ran fine when cold, but started to crap out after it got hot. His issue was with an intake gasket that was just barely making contact towards the inside, due to the heads having been shaved and the intake not, creating a mis-match in mating angles. As the engine heated up, the intake would expand (swollen as your mechanic calls it) just a little, enough to open a gap and cause a vacuum leak. Just because metals can expand, doesn't mean it will close a gap.
So you're running points and condenser? I guess it's worth a shot, but generally when a condenser goes, it doesn't store any ignition power and spark goes completely dead.
Your coil is another possibility, and I would suspect that before a condenser. A bad coil can start to make the ignition crap out without dying, been there too.

 

also...the distributor cap can have a hairline crack that doesn't make itself known at cold start but really be a bother when it heats up....when's the last time the cap was replaced?