I'm a really big fan of the Tex Beetle's layout. 4U spacebars are a rarity but it's not as if they are nonexistent. Some recent key sets have had optional 4U spacebars, including the 1976 set if I recall correctly.
Asininity, where did the white space bar come from? I'm using a Beetle at work that has a remarkably similar color scheme to yours and I'd love to switch the stock space out. I think the 4.5 unit bar on the Beetle is my favorite size. I prefer smaller spaces and the Beetles is just barely big enough that it's still usable if you've moved your hand to WASD for gaming. The tiny space on the Minila works fine for typing but it's too small for gaming.
I've been trying out using IJKL for arrows with SpaceFN recently and I really like it. I think my next board may be a 60% without dedicated arrows.
I purchased it from another use in the classified. I believe it is a KBtalKing 60% keyboard kit. However, I'm not sure where user originally purchased it from as the MD buy did not include the smaller spacebar. I could message him and see if he remembers where it originally came from.
I agree with the spacebar size. It is the perfect size for me. I've looked at several layouts for building several custom keyboards and something that puts me off is the occasionally tiny little spacebar. I wonder how much you'll miss arrows one boards without them.
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(http://i.imgur.com/L1iat.jpg)
My favorite layout is the 65% MXMini layout. Still compact but gives you the home/end/pg up/pg down and arrows back.
I absolutely love that layout. I do like the 65% as well.
This was my solution to the problem, it's not perfect, but it gets the job done for me. It's my first custom built and still not completely done, but I think you can see what I did here.
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(http://images.tapatalk-cdn.com/15/05/05/3115608087bc12f3fa991b82681fd7d6.jpg)
What's it like with such a small spacebar?