ios or android for OBD1 monitoring

[JD1964]

I'm doing an LT1 swap into a 79 Malibu wagon. I wont have a mechanical drive for the stock speedometer so that will be out of service. A while back I saw a guy who had a smaller android tablet that he had connected to the diagnostic port on his 94 Z28 LT1. He said he could monitor in real time the info from the PCM like speed, rpm and other operation data. I would like to get this ability.

Are there free apps that can do this on either android or iOS? If so what is the app name(s)? What cable(s) do I need?

I need something that works with 1994 OBD1 LT1

I have a spare iPhone 6s I could use if possible, or, I'm willing to pick up a used android device if that's better. What in your opinion would be a low cost android device that would work for this?

I know there are alot of questions so I don't expect all of them answered, but any insight would be appreciated.

Thanks