I've now ordered the smaller bolts.
A note of caution re the brackets - they get pretty rusty and they're NLA, so best to whip yours off and de-rust/paint them. NB. It's easy to round the heads on the bolts, - an 8mm socket is the best tool,* not a ring spanner. Access is almost impossible unless the road wheel is off, or you've got extremely long arms and can see round corners.
* Difficult to get on properly due to the heads being rusty.