There are a few things you definitely need to watch out for when using E85 or any alcohol based fuel in these older cars/tanks.
It tends to break down any of the built up sediment that is in the gas tank and that loose crap will end up in your fuel pump pick up/injectors and anything else with a filter.
The other issue is letting E85 sit in the tank or injectors for a long time without it being driven or used. I can't even count how many times I have had to send customers to get their injectors cleaned after letting it sit for a few months or barely driving the car.
These things don't happen to every car, but it is something to certainly keep an eye on if you do enough cars using E85. We have a station right across the street and literally have done hundreds of conversions in the past 4-5 years since they put it in. About 75% of the cars will run it on a daily basis and have absolutely 0 issues with it, but the cars that sit around for months at a time it simply gunks up and can cause some interesting issues.