Rear mount will be great as it really brings the scale of the horn down as well since you don't see the mounting flange. I was playing around with that aspect when I put together a quick mock-up last year for mine. I might need to borrow your drawing/plan for the bowtie cut-out if you don't mind. I had started it in AutoCAD but never finished it.
Have you tried tubes and more? They are local too!Hard to tell what the condition is of that original cloth from the photo but it really looks good! If it’s in good shape I’d keep it.
I’ve spent a ton of time trying to find vintage(ish) grille cloths and the cane. styles seem to be impossible to find. I must have a 100 samples and very few come close to original stuff from the day in my experience. If you don’t want that original stuff, shoot me a PM.