I can contribute nothing worthwhile to the usage of the specific camera.

I find that the most flexible method for fill flash is one of two methods both of which require the use of a flash meter. Both work best with a flash having a variable power but are adaptable to any manual flash that is highly repeatable. Luddite that I am, I alway prefer a manual system to an automatic system

Use your flash meter to determine the distance for a single given aperture eg f5.6
at 1, 2, 3 meters etc. mark these position on your power ratio device with a piece of masking tape.
With your camera lens set to 5.6 at the appropriate shutter speed and wanting to have 1:1 fill just set the appropriate distance on your power ratio device. This will on the plane of the subject that is in shadow actually give a 1:2 ratio as compared to the portion receiving both natural and flash light. For all other distances the ratio would be <>1:2

If you want to have your main light to be your flash set your camera lens to a wider aperture eg f 4 as the case may be. This will work much better with negative film than with transparency film If you are making a B&W negative you could also make your development decision here. As an alternate, set your power variatur at some further distance eg twice as far if you wanted a 1:4, in actuality 1:5 since the inverse squre law is, as always, in force.

If you wanted the ambient light to be the main light than you have two choices:
set you lens at a smaller stop than 5.6 eg 8 etc with the appropriate shutter speed and set the flash power varietur to the distance focussed upon.

Or set your distance to a distance closer to what you are focussed at. With your lens set at 5.6 and at a distnace of two meters to your subject set your variatur to 1 meter. You will again get 1:4 or 1:5 ratio.

Use your flash meter to get a guide number and test its reliabity.
Of course one can use this with a manual flash that does not offer any power level variation. Using guide numbers, with practice, becomes, in my opinion, quite easy. Just choose your aperture and place your flash at the proper distance and in the proper location for the lighting effect you desire.. It is, with experience, much easier than it might first appear.
Use combined flash/ambient meter for setting the flash and camera.