Spacer bolt size?

The thread or lenght?

The thread is an odd M14X1.5 but lenght unsure.

But to be safe you'll want at least 16mm longer than standard.
 
If you have locking bolts (like i have) measure one of your old ones in the packet.
 
You would need 41mm bolts, std ones are 25mm long (thread length) i know you can get 40mm bolts, havent seen 41mm though.

Gareth.