65 Barracuda daily driver

I give up. The new voltage regulator and new battery haven't stopped the car from stalling and then not starting until an hour or two later. Sometimes it starts after 10 - 20 minutes. I've replaced pretty much everything electrical, re-wired and soldered. I even replaced the spark plugs today. Somehow my dash lights have gotten dimmer?! Now I'm thinking that the engine itself has an issue. Like head gasket, piston rings, valves? But there's no oil in the water or water in the oil. There's no smoke out of the exhaust. Maybe a bit of a lifter tick when cold. Hydraulic lifters. It runs great on the freeway, just not idling great. If it's the engine, I wouldn't even be that horrible, because I already have a new engine sitting in the garage. Just waiting for the transmission to come back from being rebuilt. It was going to be 2 weeks and now it's over two months. I hope to get it back this weekend. The following weekend I have plans, but the last weekend of the month I can hopefully pull the engine and swap the 318 in. Not having a reliable car until then is not great. Sorry for the rant, but I'm considering to buy a beater for the meantime, because I need to be able to get around.