Hi Bali. Congratulations and welcome. As far as I am aware, all W113's left the factory with handbrakes placed on the left side of the tunnel. The easiest way to address the accessibility problem in RHD cars is to fit retractable seat belts, which enable the driver to reach forward without unbuckling. If you really do want to move the lever to the right hand side of the tunnel, I believe it can be done. In fact, there is a recent thread on the subject, as started by one of your compatriots, whose 280SL already has been modified this way. I will try and locate the thread for you.
With regard to door lock striker plates, these are a problem. Please have a look at the thread I started on this subject last month. Replacement strikers are readily available for 230SL's and early 250SL's, as they are for late 280SL's. Unfortunately, striker plates for late 250SL's and 280SL's up to July 1969 are very hard to source. For a full explanation, have a look at the relevant technical database on this website and the SLS.de spare parts website.
Regards
Pip1947