banjo,
Firstly drill some strip brass to be a tight fit over the inner propshafts and the width of the propshafts. Put these formers over both ends of the inner propshafts.
I then soft solder some brass strip (at least 2 of) between the outer propshafts. This makes the propshafts fairly rigid and more importantly parallel.
Remove the outer former and open up the hull to a good "sloppy fit". Mark up the "A" Frame holes in the hull, again a good sloppy fit, as previously described bend the legs that protrude into the hull so they are straight through the hull.
Fit the propshafts through the hull to about the right place and slide in the inner propshafts through the outer propshaft and "A" frames.
Lock the brass strip aft of the "A" frames with 2 nuts on each shaft, this should make the whole unit quite rigid.
I then place the motors and couplings roughly in place to ensure that the motors can be lined up when the propshafts are set.
Loosely screw on the props.
Now measure, measure and check the measurements to where you want the props to sit and the "A" frames, ensuring that the shafts are parallel to the keel of the model.
When you are satisfied that they are in the right place superglue the outer shafts into the hull, use the glue sparingly.
Put to one side and let the glue harden and all solvents evaporate, overnight is usually good.
When you return to the model check everything again and check there is no binding in the "A" frames.
If you are not happy with the fit remove the shafts and start again.
When happy with the fit tape over the holes in the hull from the outside with masking tape.
Mix some epoxy resin and run around the shaft exits and "A" frame exits, just a thin smear.
Again let harden.
Now you have rigid propshafts and "A" frames.
Quickly check everything is in place, if it is you can now make them permanent using either P38 or Epoxy.
For Epoxy use a small amount of blutak to hold in the epoxy.
Either bent or cut off the excess "A" frame inside the hull.
This gives a very strong rigid system where I have dropped a model on the props, bent the "A" frame, but all stayed rigid in the hull, so straightened the frame with pliers.
Remove the masking tape and fair in using P38.
Bob