RBA/TRA What Rifle best suits a Class 1 Benchrest Sporter Rifle that could be used to accommodate both sets of rules.

The only rules of TRA I have found are:
CLASS 1 – BENCHREST SPORTER RIFLE.
1 Be a rimfire rifle, chambered for the .22 long rifle cartridges.
A magazine maybe used, provided that the reloading of the
cartridge into the breach is by manually pulling back and
replacing the bolt.
A.5.4.2 Have a barrel with a minimum length of 460mm measured
from the face of the bolt to the apparent muzzle and cannot
be fluted for Class 1
TRA Class 1 Benchrest Rifle is any rifle chambered for .22
rimfire long rifle cartridge having a safe manually and
mechanically operated firing mechanism which does not
include the use of pressure fluid, gas or remote control.
The weight of the rifle shall not exceed 3.5kg inclusive of
sight and unloaded magazine (if applicable).
The width of the stock shall not exceed 60mm at any point
and the fore-end shall clearly have a convex shape.
Nothing may be fastened to the barrel except sights and sight
bases.
Any telescopic sight shall be limited to a maximum of 12
power magnification. Variable magnification telescopic sights
to be set at or less than 12 power and taped by the Range
Officer or equipment control.

I was told that it has to be an off the shelf rifle with no customizing but that is not what the rules state as far as I can read. Is there something I have missed ?

RBA equivalent grade or rules not sure ?