I have not built one myself, but I do know what needs to be done. I just finished my Alternative Fuels class in college and I got an A so here goes. First, you will need special alcohol compatible seals and gaskets for the carb and fuel pump. The hoses and lines may need to be changed too, generally to stainless and an ethanol resistant rubber. Most fuel injection hose nowadays should be fairly resistant to it, seeing as ethanol is blended into most gases available. It is also safe to run much higher compression and timing, this helps offset the power loss from E-85. 12.5:1 up to 14:1 is not unsafe or uncommon with this fuel. You will also have to rejet your carb about 30% richer too, as E-85 has about 2/3 the energy of normal gas. You may or may not encounter issues with your fuel sending unit because unlike gas, ethanol is electrically conductive. E-85 can have cold start and drivability issues too even though it is much more volatile than gasoline. I think that about covers it, I'll post more if I forgot something.
