Since you don't have a square factory hole in the dash you can put the switch anywhere you darn well please. Moving it to the LH side of the dash is an excellent idea. Rather than cut a square hole for the GM rocker switch just drill a 1/2" hole and use a toggle switch...
If your solenoid valve is working you can use a six terminal DPDT toggle switch on the dash. Try to find an ON-ON switch rather than an ON-OFF-ON... You can use either but obviously ON-ON is more intuitive.
Clip off the outer 45° terminal corresponding to the blocked hole in the stock 1973-1980 switch plug that GM used as a key.
You can get Generic DPDT toggle switches with six 1/4 disconnect terminals from McMaster Carr and many other outfits. I'd get one that carries a minimum of 15A continuous. 20A or 25A would be better.
If you need to run the 1981 and later motorized valve you can get a four terminal Polarity Reversing toggle switch with 1/4 disconnect terminals that can use the same connector shell as the 73-80 switch.
A Polarity reversing ON-OFF-ON toggle switch that will carry 25A operating current is Cole Hersee 55046. Waytek Wire carries them.
https://www.waytekwire.com/item/4426...BoCeO0QAvD_BwE
Keep in mind that the Polarity reversing toggle switches you can buy have a centre off position. This can be useful on 1987 & later TBI fuel pump systems as a theft deterrent... Setting the switch to the off position shuts off power to both fuel pumps til you select one or the other and it's not easy for a thief to find.