Hi Lee,
Usually the chain has to be an original style with narrow sideplates, the "H" chains will foul the rear primarycase
Make sure it is a quality made chain not industrial type,
I have been fitting "Regina" brand chains for some years now
Some A10's were lower geared and used a 69 link chain that needs a half link
70 links is correct with 21(?) 22 & 23 tooth engine sprockets
HTH
John