Which constructors have built F1 AND Indycar machinery?

I don't know the exact details, but Honda did have a design team in-house, including Dr. Harvery Postlethwaite (ex-Hesketh, Ferrari and Tyrell) and most of the Tyrrell F1 personnel. They didn't have fabrication capacity and may not have had any wind tunnel facilities in Europe, so Dallara could have had serious input in these areas. Honda pitched in the ideal of a works team when Postlethwaite died of a heart attack.

But, remember that Dallara ran their own car in the early 1990s as well.

ClarkFan

Dallara only built and designed the car. It was commisioned by BMS Scuderia Italia.

http://www.grandprix.com/gpe/cref-lucgiu.html