I think the hardest part is going to be finding someone who actually has Ernie Alston's integrated simavionics (ISG1 - payware) gauges set AND integrated it into the 727.

A good program (unfortunately it's payware) is FS Panel Studio. You can open the panel.cfg with it, highlight a gauge and select "swap" which would then allow you to choose one of Ernie Alston's gauges. I don't know how it will look, Captain Sim's gauges are made to fit in the 3D models they create.

Your workaround would be to create a 2D Cockpit for both the 727 and 707 and use Ernie Alston's gauges on that.

Mark