I'm sure my MOMO boss was 6mm so I drilled the steering wheel accordingly as I didn't fancy using 5mm bolts in a 6mm hole that's why I tapped the QR boss. The steering wheel had already been drilled for countersunks
See my posts on this thread, there is a link to the race team I purchased mine from
https://www.caterhamlotus7.club/forums/topic/272475-which-dzus-tool/#comment-271963
For those that don't have a heater I fitted a combined toolbox/jack on the engine bay shelf. This was fixed via 4 rivnuts into the shelf and further secured by 2 long bolts with penny washers through the bulkhead and rear of toolbox.
I think your order is correct and yes my top hat sits on top of the boot cover. This enables the harness to swivel, the crinkle washer simply stops it rattling and the boot cover will sit flush with the chassis rail. I can’t see how it would work if you put the top hat under the boot cover…..
According a Demon Tweeks blog on understanding helmet standards a Snell SA2015 expired 31.12 23 but a dual standard FIA 8859-2015 & Snell SA2015 has no expiry date which suggests that an FIA standard is greater than the SA2015 as advised to me by MUK.