There have been some 10-watt halogen bulbs the make maybe too much light for the larger dash instruments (takes a lot of getting used to), and some 5-watt halogen bulbs that are bright enough (and may work well for the smaller instruments). They work will, make a lot of heat (which is okay here), and must run at full voltage all the time. Do not dim the halogen lamps by reducing voltage, as that would reduce the bulb life dramatically).

Now we have simple 6-watt incandescent bulbs with E10 miniature screw base, Westinghouse number 03797. It has larger globe diameter, but should still fit for plug-in socket instrument lamps. Cheap at $1.89 (2 pack) plus shipping from LightBulbs.com

6 watt - 12 volt - G4.5 - Miniature Screw (E10) Base - Clear
Might be as low as $1.59 (plus shipping) for a two pack
UPC Code:   030721037979

Light Output:     40 lumens
Energy Used:      6 watts
Average Lifetime: 1,000 hours
Volts:            12
Bulb Type:        G4.5
Base Type:        Miniature Screw (E10)
Filament Type:    C2R
Color / Finish:   Clear
Color Temperature: 2,700K