@Mcbhaine by the way I ceaselessly scour eBay, Facebook marketplace and gumtree for stove parts for some of my stoves so if I see that winged riser I will be sure to let you know.
I believe @Firestarter is correct on the leg size. If memory serves correct this was #6 drill rod from a nut and bolt hardware store. I drilled the threads out from a nut and slid over the leg to braze in place. Not an exact replica, but it works well enough for me.
I join those interested in what the bottom stamping is on this one. It is another key detail for early undated Optimus. It was easy enough for @Mcbhaine to send it on to me. Thank you, that is much appreciated. Here it is: