Hey Eddie,
I cant see any room in this welder unless i mount it outside at the back maybe? At least i found tge leak on the gas couple in side the machine i used leak detection fluid you can see the bubbles in one of the attached pictures
Good that you found the gas leak! Maybe the original torch is going to be OK now, and you'll not bother with the swap?
Perhaps the gas solenoid would fit on the other side of the steel dividing wall, in the top left corner, above the spool of MIG wire?
You will also need to find space for the Solid-State Relay. It is about the size of a matchbox. It can be screwed to the steel case, but that is not essential. It is a 25-Amp unit, but will only be passing about 0.25A to the gas valve, so does not need a heatsink. However, the screw terminals 1 and 2 are at mains voltage, so need to be insulated.
At the front panel, you also need to find space to install the Euro socket. If the panel is steel, there has to be clearance around the brass block and tube, which will be "live" with welding voltage.