I would rather keep them on the looser end of the spec than tighter end, the straight six is Yamaha designed and follows the same pattern of shim under buckets like the Yamaha 750 engine I had on my FZR-750.

__________________
99 Gurkha with OM616 IDI turbo

2015 Gurkha with OM616 DI turbo

2014 Rexton W with OM612 VGT