Different part numbers, though, with only the J2 appearing to have the fixing clip and bolt. I have a recollection that the J1 fairing may have been secured to the front cross tube by Terry clips. Does that ring a bell with anyone?
Edit: This factory photo clearly shows the octagonal bolt on the J2 but nothing similar on the J1 so perhaps the j1 valance came with clips attached and no hole for the bolt - hence the different part number? J2 fairings cost 16s, J1 ones cost 17/4d.
Thanks to Ted Hack of the excellent MG D Group I am able to share this extract from their ‘Dispatch 11’ .
I think it is a reasonable to assume the D and J1 aprons were the same. The J1 apron appears to be basically like the J2 but with the addition of mounting clips and provision for a horn.
Sports Car Metalworks (Michael Beakhouse) list J or P MMM front aprons amongst the many panels they manufacture and would perhaps make any small modifications required for a J1.