I've got some gallon jugs of reagent-grade ethanol. Can I dump these into my gas tank--like I do w/ xylene and toluene for an octane enhancer, or would EtOH not mix well?
It should mix okay as long as the gas tank has no trace water in it. That being unlikely given the age of the vehicle. The E85 also includes some corrosion inhibitors etc.
If you make an effort to get things mixed, like pour the Etoh in, and then top off the tank with gasoline, or go a bit easy for a few miles so normal driving stops and starts turns etc. give the fuel time to mix well, I wouldn't expect to have much problem.
As always with the do it your self stuff just like the toluene there is some small risk of mishap. For most of us its much easier to get the E85, as unless you have a direct connection to an industrial user of ethanol its not cheap if its not denatured due to BATF regs.