Converting single seat ex-police BMW R1150RT to dual seat

there are bmw dealers with s/h spares,a lot cheaper.try motorcycle news for adverts

yes i know were you can get all your parts from,,,
have a look on ebay,, its full of bmw parts

NGK's are good. I would stay with them .
Try getting them at an auto parts store. (You will need the #'s)
I've had luck on getting them cheaper.

to Rideonronm;
I bought one of these ex police r1150rt,s 3 months ago
& thought i had a blown fuse for the heated grips- fuse box under the seat by the way-,turned out when the police de-commisioned the bike,they cut both 12volt wires going to the grips. My solution was to take the fairing off & re-connect both wires.....works fine now.