Hi Tony,
Thanks for the info.
I can say confidently that the car will be finished after Christmas...... maybe not this one though!
I think you are correct about the 7/16 window channel being fitted only to the later models, the bits I removed looked pretty original and there were also some fairly newish looking bits of felt in one side of the car where the original channel had corroded away and I'm guessing that Terry may have replaced these at some point when he owned the car.
I've tried a few experiments now and some results as follows.
A. 10mm x 10mm channel flock lined on the inner and outer faces - once I fitted a complete length this fitted very nicely, nice snug fit in the chrome frame and looks really good, As Luke pointed out though the glass is a tiny bit loose in the channel, (available from Vintage Supplies 263A - window channel)
B. 3mm thick x 25mm wide felt - This also fitted nicely in the window frame and looked pretty good, it didn't feel quite as secure as the 10x10mm channel though, but it was a better fit for the thickness of the Aceca window glass.
C. Would have been making up metal U channel and lining with felt, but to be honest both the above options turned out so well that I decided that it would be a waste of time exploring this option.
Hope this info will be of help to someone in the future.