Prototype came back this afternoon, new front standard is easy to use. Here two types of front standard sit side by side, with circular/ rectangular lens board accordingly.

New front standard has a sliding lock at the top, it is big, so you can grab it with fingers very easy.

You hold the sliding lock and pull it upward, that release the lens board, you release the lock, with help of springs, lock slides back and locks the board, that easy.

Front view of prototype, light trap around lens board keeps light away.

Like I said before, this front standard is great when you use big eyes, here are what I tested.. two Xenotar 2.8/150 with #2 shutter, one Xenotar 3.5/135 with #1 shutter, one Tele Arton 5.5/270 with #1 shutter, one Super Angulon 8/90 with #0 shutter, one Grandagon 4.5/75 with #0 shutter.
Only Xenotar 2.8/150 needs to be mounted in-directly, others all are capable of directly mounted.

Thanks to NY Jeff, push me to solve problem mounting Xenotar 2.8/150 on Byron, without him, I would not make it!

This is the biggest lens Byron can hold, rear element is too big, can not mount the lens directly, what a pity.
Funny thing is that almost emails came asking about Xenotar 150 are fashion photographers, but that make sense, this heavy big lens is too bulky for snaps.

Tele Arton 5.5/270, very easy to mount on, but I need to test the rail limit.
And for Grandagon 4.5/75; SA 8/90 and Xenotar 3.5/135, this front standard is easy to mount directly.
Now is time for minor modifications, round corners, dimension adjusts......
and matte black surface paint.