Not sure which adaptor you mean but they seem to be available.
Will have to look at mine and see how the standard ones are fitted.
ADU710050 SEAT BELT ANCHOR BRACKET | shop | www.lrseries.com
MTC4090 INERTIA SEAT BELT MOUNTING | shop | www.lrseries.com
As mine currently has tatty belts it's just a swapover so the Paddocks ones are a big saving over local prices.
Colin

