Oh, the bad news; the "194/168 bulbs used on Pantera are different from Mangusta, aren't they ? I think Goose uses older style "1893" bulbs with bayonet bases, note that PanteraElectronics mentions '71 Pantera cannot use their hybrid white/green LED. The good news, LED replacements for these are dirt cheap.
I think, do NOT use an LED in the GENERATOR warning light--I'd think this requires the traditional incandescent bulb (not just as an indicator (where the bulb is bidirectional for current and proportional illumination depending on the amount of difference between the battery and alternator), but also because the bulb appears to be one way for current to flow back to alternator voltage regulator and "field" supply....so I'm reading). Using for the turn signal is probably OK (at least, even the mechanical thermo-blinker timing relies on the current draw of the outside indicator lights, but not on the single bulb output in the Gauge).
...Veglia gauges are not all that hard to take apart...But crimping back the bezel without it looking like sin is another thing! If I can be of any help, it is to give you some peace of mind that opening up the gauges is Not going to help a lot...
First regarding the power---my reference is are laptop computers, which will typically consume about 3 watts with the LCD half bright and doing nothing. But each of the 6.3v bulbs will take 6 watts, with virtually of all of converted to heat. So with 10 bulbs in the dash, by my perspective this is quite a lot of heat...The good news, it will give the rheostat more range .
But also, unless you would actually wrap the back of each movement in the gauge with reflective material, I see no practical way to improve the optics. The path from the bulb causes the rear of the movement area to be well illuminated, and only by chaotic reflection will anything leak around the rim. But since the movements themselves are non-reflective, there is not going to be any recycling of light inside the can--meaning, most of the light will simply be absorbed by the movements. Finally, what little escapes around the dial itself (and this is a small gap, about 1mm) gets redistributed onto the dial face.
The interior of the can itself is painted white. If you have the cans open already, it wouldn't hurt to freshen up with a new blast of white ...But for example, on LCD displays the recycling reflector behind the Light Guide is almost always Only a white material (not silverized). But at the core, these gauges are incredibly primitive optical designs and (short of actually bonding side-firing LEDs around the circumference of the light guide at the front of the dial) just blasting with a stronger source is where I'd suggest leaving it...Lee