If you look at the photo, the LH silencer is closer in than the RH causing the centre-stand foot to foul it (the silencer support bracket is not bent).
I have a 1969 A65.I had an issue with the center stand fouling the LH silencer.It happened when I replaced the original BSA headpipes,with a set from Armours. Their pattern, primary side pipe, was straight,not kicking up past the primary cover. Here are some pictures,(4), two on a dark background, from an ebay ad,showing the kick up,similar to my factory pipes LINK
1969 BSA A65T w/A70 engine 1970 Royal Enfield Interceptor S ll
Been a long while since I played A 65 but that brake arm looks way too long to me . AFAIK all BSA brake arms are interchangeable as they all have the same size square machined on them. It might just be the angle but the anchor strap looks a little on the short side as well. the brake cam sits vertical above the axel and the rod runs above the axle. Me thinks the brake arm might just be a front one fitted to give more leverage to compensate for a short pedal which would have been fitted if as previously mentioned the bike had rearsets fitted.