Best to check with Justin from Speeder about the headset to be sure.

Also, the cable exits below the bottom bracket don’t really make sense for anything else besides shifting cables if i look at their diameter.

What else would you route below the BB apart from shifting cables?

Have fun building up this frame 

Here are some pics. It's a nice frame. And since made with EPS, there is no wrinkling and bladder remaining in the frame. Frame weight is including 4 bottle cage bolts and both derailleur hangers (ca. 40g plus ca. 20-30g for clearcoat). Bare frame without paint will be around 810-820g.

Why is that?

I ordered another frameset (Elilee Blize) in the meantime so I'm probably not going to need the SC-R48D.

I use this one in size 360 since it is the smallest I could find and I needed the central hole in the clamping area as well

https://de.aliexpress.com/item/1005004517090262.html?spm=a2g0o.order_list.order_list_main.29.4d4f5c5ffSkaZn&gatewayAdapt=glo2deu

Weighs 221g and the quality is fine. I also use one for CX.

I received such a frame from a friend of mine. One of the aluminium BB inserts de-bonded from the frame and since he wasn't too happy about the stiffness of the frame either, he decided not to use it anymore. I could do whatever I wanted with it (I build and repair carbon parts on an amateur level). So I cut it in half.

I will post some pictures later, but a few comments first:
The frame was incredibly light, 728g for a size 54 to be exact (no typo). Since I highly doubt that HM fibers are used in such a frame, I suspect that they simply reduced the amount of stiffness layers to achieve such a low weight. Or some precut pieces fell to the floor and the person laminating the frame decided not to use them anymore That's also in line with the owner's feedback who said the bike felt pretty noodly.

The good: The frame is surprisingly well built, the inside in general looks very clean. No wrinkles and almost no voids.

The bad: The rear dropout for the derailleur hanger I find horrible, it is so thin. This was mentioned in this thread already. The connection where front and rear triangle is glued together is done poorly too. You'll see why on the pics. The integration of the seatpost shape in the seattube isn't a showpiece either (an OEM SL7 seatpost doesn't fit, BTW). The BB area is pretty thin compared to other frames that I cut and honestly, I'm not surprised that one insert decided to part ways.

Would I recommend buying such a frame from a manufacturing/engineering perspective? Absolutely not. I'm not squeamish when it comes to carbon parts but IMHO I'd stay clear from such a frame.

I just ordered an SC-R48D frame. Justin is very easy to work with. No language barrier, quick answers.

Carbon gloss finish, size 520, 849 USD including shipping. According to Justin, about 2 months lead time.