Manfrotto to Arca Swiss - 732 CY with A3RC1
Those smaller Manfrottos are unfortunately a bit of a dead end street. I think I'm right in thinking that neither the head nor the QR clamp are removeable. In which case there are three ways of doing it.
1. Get a cheap Arca-Swiss clamp from eBay and attach the clamp to your manfrotto QR plate.
Although cheap, I wouldn't recommend this. It would probably require some sort of butchering of your Manfrotto plate and the additional connection between camera and tripod would probably undo any benefit in stability of the L bracket.
2. Although the head is not removable, the centre column is. You could replace the centre column with some metal tubing and use some epoxy resin to attach a threaded bolt. See this site for more detailed instructions. You will then need to buy an Arca-Swiss compatible head.
3. Sell your tripod and buy a new, Arca-Swiss compatible tripod/head, but spend a little more next time.