Hi,
Go for the softer SS materials, the 316 can crack with vibration
I used 10 x 8mm for the front stays, I sleeved the ends with a couple of inches of 12 x10 before flattening
run a 10mm drill throught the larger tube first and it will tap on
This was so it looked similar to the way the originals were made, also stronger!!
When making plain stays from tubing I put a piece of flat into the tube before its fully squeezed
This gives it a lot more strength.
I use two pieces of alloy with a semicircle cut out of the sides and squeez the tube between them to put a radius on the transition , this prevents cracking at that point
HTH
John