Shower inlet valves need rotating - how to seal?

[Brotheroak]

I am replacing a leaking shower (cartridge no longer available!) with another shower that we are otherwise not using.
The replacement shower valve (concealed thermostatic) has feed inlets pointing upwards, as the feeds were originally coming from above.
The new feeds are coming from below, so I need to rotate the H and C inlets (90 degree brass connectors) on the shower valve by 180 degrees.
They are on screw threads and were originally sealed just with PTFE tape, and tightly screwed in.
I've taken them apart to renew the PTFE tape, hoping that I would either put a bit less tape on and turn them an additional 180 degrees, or a bit more tape on and they will tighten earlier, in order for them to point down. No luck as the thread is quite wide, so pointing down they are still loose.

My question is how would this normally be dealt with? I can't imagine the original shower didn't have an option for the inlets being either fed from above or below (no markings on shower or valve, so no idea of the model or even the brand!)

Do I simply use a fibre washer to pad out the thread so it seals in the right position? The screw threads seem to be 3/4" diameter with flat mating faces

 

[cross thread]

Locktite 55 should sort it

 

[Madrab]

Alternatively, use gas PTFE tape, normally 7 wraps. Take the fitting with nothing on the threads and see how far it screws on before reaching the end of the thread. Mark the threads with a pen. Wrapping the male end and using the mark as a guide screw the fitting on until nearly there but the fitting is pointing down. That should feel quite tight and be more than enough to make it watertight.