I have bone stock 69' 350 with 2bbl and stock highway gears with non posi. Rebuilt but not overbore. I can do a decent 1 tire power brake. What a sad statement that is lol! Sometimes it will give a nice chirp off the line and maybe even a solid spin. And yes she love a little gravel.
However I would very much doubt you are making 300hp unless the heads have had some work. What heads are you running? The stock 68' 350 heads are #17 which is real good 350 head. But don't waste your money on the 93 gas. 89 or 91 will be fine. Hard to say if the 4bbl is even helping you? With that gas mileage it sounds like it is tuned well so maybe. It might actually bog a bit when you stomp it off the line until it builds enough RPM to use that extra gas and get those heads flowing.
As stated above you will need to change gears to get those tires going. A nice 3:08 set with a posi will do it and be fine on the highway and give you some nice get up.
