Primal and et al
I've been looking at e-85 for power for a while.
First, your 250 with .030 overbore, .005 deck clearance, and flat-top pistons 54 cc combustion chambers equals a 12 to 1 compression.
If you do a 46 cc chamber you'll get 13.1 to 1
I am using my web compression calculator at
http://falconperformance.sundog.net/compcalculator.asp
Try it out
North Dakota and Minnesota use 10% to 15% for ethanol/gas mixture. It is hard to find just gasoline. E-85 is plentyful. My '60 Ranchero has used it for 8 years. The only
really irritating problem has been MELTING the paint around the gas filler neck. I had rebuilt the carb. I have not had ANY problems with the fuel pump. I had my gas tank cleaned when I built the car (Iit had been flooded to the inside rear view mirror in the great flood of '96) I still have to change the fuel filter each spring. I'm at about a 9.3 compression.
As previously stated by others, you'll need to run 20% to 30% richer.
You'll need to rebuild the carb with a kit capable of withstanding e-85.
The more compression, the merrier. BUT you can't easily lower the compression. Premium gas with 105 octance booster would get you home if you couldn't find an e-85 pump.
Good Luck