Series 3 Wiper arm problem on S3 lightweight

Morning all. Finally got a new vent panel on my lightweight and it's all just about back in one piece, except the wipers! I've bought new wiper arms, and new splined adaptor drums, naively expecting it all just to slot together.... Of course not! The wheel box spindles on mine are totally round and not ones with flat faces that I've seen mentioned. But the adaptors that I found don't fit as they haven't got a round hole through them and instead look like they're designed to slot onto the flat-sided spindles.

So far they're the only type that I've been able to find online which is pretty annoying. Just wondering if anyone knows exactly what I'm looking for. If anyone had a part number or anything that'd be amazing.

Thanks in advance and hope you all have a great weekend in the sun! Cheers.

Is it possible to drill them out.
Must admit, never seen round ones.

Grind or file a flat edge on the spindle?

Cheers guys I had been thinking of grinding a flat edge on the spindle but was going to leave that as a last resort. But actually maybe there's not too much to lose by giving it a try. I'll just go very carefully with the grinder!

Just got to grind a bit then try and repeat. From memory there was quite a lot of tolerance on those things so you won't have to grind off much. There's a lock bolt to hold everything tight

Mask off the windscreen just in case, if you get sparks they melt into the glass.