[exray]

The lead from the Feild coil 62 was tied to the filament of the 80 tube, this is a separate winding from theothe filaments. Neither lead of this winding is grounded.
My first ? is can an 80 tube replace a 84 without making some changes?

The most obvious difference between the two tubes is that the 80 has a 5 volt filament and the 84 is a 6.3 volt filament. Since you indicate that there are separate filament windings maybe that power transformer replacement was part of the "fix" since the stock xfmr in the schematic does not show a 5 volt secondary winding.
Its not an unreasonable repair although its hard to say which was the chicken and which was the egg. My thoughts are that the previous guy had to replace a defective power transformer with what he had on hand and that resulted in having to go to the 80 tube rather than vice-versa.

But who knows??? Since that type of change has been made it would be worthwhile to confirm all of the voltages and make sure they are still in the intended ballpark. I don't see any need to replace the power xfmr (your ? #3) if its working.