Unleaded gas

Tryathlete,   a follow up, the Mag Phosphate was never used on Valve Seats, it was used in Valve guides, the first application I remember for that product in automotive use.

You and your three brothers actions sounds exactly like my house with two older and one younger brother. We did not have the street lights but it was common for our friends to light up the tires leaving my mothers house.   It made our neighbors mad and my Mom liked all the boys but was fed up with the tire burning.
A buddy Gene bought a 69 Chevelle SS396, 4 speed, 4.11 Posi, this was about 1972 the car was beautiful.   He was at the house and my Mom knew Gene was going to lite em up on his exit so she walked outside and said, Gene, if you burn those tires in front of my house you can't come back! Gene smiled and swore he would not spin the tires in front of your house.   Then he eased away in first gear, once in front of our neighbors house Gene shifted to 2nd gear and lit the tires up for about 100 feet in second, even my mom laughed because there were no tire marks in front of our home.
With 4 boys it seemed we always had one car being fixed on the driveway.   
Your choice of a 340, 1970 engine was a good one, that 340 was probably the most powerful small block engine produced back then because of the X heads it used.
Those were very quick cars and the engine was durable.

So after reading most of above post, I will fun non-ethanol unless can't find then med grade .