What's the screen angle like on that Sony in the dash ?
I've not had it all together yet, so I can't say 100%! Last night it was lying all over the passenger seat with wires all over the place. I tried an L pad attenuator circuit in front of the transformer to try and reduce the head output level a bit. The Sony outputs 5volt line outs, and the Clarion 0.125volt so I thought it's blow the doors off. It didn't though, so I don't think you need them. I don't know much about electronics though, so I might be wrong!
When I do final soldering etc I'll omit them, and just have the audio transformers with a 10K resistor accross the secondary windings. The stereo unit in a p38 is resessed about 30mm behind the cubby box thing, and the Sony unit has enough "reach" for 20mm, so I'm going have to work that out.... It tilts to 10 degrees up and down so I think it'll be fine. I'll let you know!