Hey all, thanks for all your comments. Sorry for the late reply, when I tried to comment yesterday it said I could only post 5 times a day.

For now, I've ordered the suggested treadless YST bottom bracket off of eBay (Made sure it was YST). It'll take a couple weeks until it arrives, but I'll keep you all updated!

verktyg I'm afraid you're right about the original BB being removed, it really does look like it. I'm not sure how many previous owners there were for this frame so it'll be a complete mystery as to why it was removed.

I'll have to chase the Mavic treadless BBs if the YST one is a bust, but at that point I might consider just getting a different frame.

dddd Thanks for pointing out the spindle length. I did indeed order the wrong spindle length for my FC-1050 crank haha. I'll try to get the order cancelled and order the correct one. Do you think 1mm will make a big difference? I'll need a 115mm spindle, but I can only find 116mm on eBay.

edit: I just found the manual for my crank online. it says I'll need 115mm for a 70mm bottom bracket (113 for 68). Does this mean I'll need a 68x113 bottom bracket? Sorry for the dumb question, my brain is absolutely fried and somehow I can't figure it out.