NGK R5671A-7 or a -8 ..... this is a 3/4 reach flat gasket pug.... 7 is hotter than 8 ...9 would be to cold for you... depending on your cam 7 may be a little hot... I run a 8 heat range with 15lbs of boost so I would start with a 7 and read the strap with full timing in.
I use to buy e-85 at the pump but found issues with gas stations, E85 can absorb water because of open vents and depending on how fast they replenish the tank, the water will not separate until it reaches a threshold . Next problem is e-85 pump fuels then to be mixed with the cheapest gas they can find . They call that gas "drippings" and its not good gas... the 15 percent cheap drippings was the probable cause of the black gummy residue in the intake manifold which I had experienced. I was told by a manufacture they also use a friction reducer for the gas portion made for transporting the gas in pipe lines which may have contributed to the black gumming, or it was possibly related to the two fuels separating out from one another during the liquid to gas phase in the intake manifold
.
For these reasons I will only buy a pail or a drum of E85 from Ethanol one to avoid the black gum and water in the fuel.... You have to use a hydrometer to check specific gravity to know if there is water in the alcohol. You have to know what specific gravity spec from the manufacture in order to test for water content.
Always keep your tank or fuel seal sealed until ready to race or drive or in a few days with an open vent you will have some water in the fuel because it does suck water from the atmosphere.
I learned these things the hard way and hope it helps someone.
Best
Jeff

Thanks for that heads up, much appreciated. What state are you located in ? Out here in So.Cal the fuel regulations are very strict, which hopefully translates to a more consistent E85 blend ? We shall see.. My neighbor has been running a 13.5-1 408 small block stroker for 2 years on pump E85, when I asked him about his experience he said "Great". ." Just keep the tank full and don't let it sit for longer than a week without driving it". Do you run any type of fuel conditioner ? I've been told the Lucas stuff works well. Thanks for the plug info too.