Who's the A body fender tag deciphering guru? Question about a car in the"For Sale" area...

Since everything is out from under dash and engine compartment has fresh paint it could be the firewall was converted to AC? Without H51 on fender tag that firewall needs a close inspection. And what all parts are included or missing is not clearly stated. Floors underneath have fresh paint. Car needs an in person inspection. Car looks like it has a lot of potential though.