There use to be available a vaccum gauge type Fuel Economy gauge you could "T" off any manifold vaccum port. But as for a electronic type air ratio gauge I dont think it would be possible without the proper sensor feedback you get from modern electroncs...Its like trying to hook up a OBD II scanner to a '70s model car. Unless you have the CPU and data link its not going to do you any good.
kinda like taking my T/A in for its last safety inspection for tag renewal. The mechanic was in his early 20s and came and got me to ask where the data link was hidden, because he could not find it under the dash and he knew I had to had moved it.
