Following up on this. I also double-checked with Spektrum and they suggested the new ones, not the 9646's.
They were already available in December, so I bought 4 and installed them 2 in the nose and 2 in the tail.
Spektrum advised not to lengthen the leads to more than 36'' so I bought 2 36'' extensions and installed the rear ones as far back as possible.
I maidened the model last Saturday (after a scrupulous range check) and it all went fine.
Thank you for your help,