mx5_97_turbo

Question 1: I just bought a mustang with a built 331 and Holley 750 carb. The car won't idle until the water temp is at least 140. Once warmed up, it idles fine. Here is a list of mods the previous owner did:

331 stroker motor all forged internals
edelbrock rpm heads
edelbrock rpm air gap intake
crane 1.6 roller rockers
holley HP seres 750 mechanical secondary carb
lunati cam # 51014 500 510 lift 284 292 duration
lunati billet steel timing chain
bbk equal lenth headers
flowmaster exhaust
ford motor sports aluminam rad

Q 2: The car doesn't have hoses running to the heater core, so I don't have heat. On top of the water pump is a threaded plug. I need to replace this with the nipple for the hose. Where can I get this nipple, or what is the thread?

Q 3: Why is my gas mileage so horrible? I wasn't expecting 25mpg. But the car has 2.73 gears (yes, 2.73s, not a typo). At 70mph, the rpm is maybe 2k. Driving almost all highway, I'm only getting 12mpg... Can the carb be tuned to fix this?

Q 4: Considering I want to use this car as a daily driver, would a different cam make the car more street friendly? If so, what would you recommend? Or can I just adjust the carb?

Thanks in advance for any help and suggestions.