classic ignition switch problem.

Hi all,
I need to fit a replacement ignition/steering lock assembly to my RR classic , but its a jap export '92 model with a different part no. due to a shift interlocking feature (ntc9440). Can I fit an alternative part (i.e. prc8907), and disable that feature, and for that matter what does the shift interlock do ?
The problem I am having , is that the key is difficult to insert ,and the key sticks in the start position making the starter motor run on , and sometimes I can't get the key to turn after insertion !
cheers, bob whild

Problem sorted ! I purchased a lock assembly off ebay for £9.99, removed the electric part of the assembly and swapped it over, using my existing electrics ! It was completely compatible . Thanks anyway .By the way , I didn't need to drill out the shear bolts .I just hit them with an old screwdriver on the edge , and they started undoing !