It can probably be done, but will be easier & probably even cheaper to use Torco Accelerator octane booster.
There are lots of E85 Holley carbs & kits.
There are big Roch-to-Holley adapters. I suppose this would allow you to use E85 Holley 2-barrels. ???
There are a few guys who build E-85 Q-jets. So, I assume there are guys who can build E-85 Roch 2-barrels. But, it usually involves more than just a jet size increase.
e85carbs.com will convert your Roch 2-barrel. This quote is taken from their website, near the bottom of the page.
" Convert your Rochester 2brl to E85 We can convert your 2 barrel carb quickly. This includes normal replacement parts for E85. If your carb needs an overhaul we can get that done for an extra charge. We can convert most 2 barrel performance carbs.
Purchase your conversion here with PayPal or credit card, print out your recipt and Ship a copy with your carb and send it to us at: Rob Mix Services, Inc.*465 North Street * Saint Paul, MN 55130. This overhaul can take 1 week in shop but we try to turn it sooner if possable. Return shipping will be added at checkout about $24.50 "
Several carb shops build 2-barrel Rochs for circle track racing. They use high flow needle & seats, small floats, and are drilled for Holley jets, in order to flow more fuel. So, I figure one of these guys could build a good E85 Roch. I'd talk to SMI about it.
Also, the actual ethanol content of E85 can vary greatly, from area to area, and can change from season to season. If you switch to E85, you need an ethanol tester, in order to verify the ethanol content, before using it.