Bill Daniels wrote:
I think your question was about panel layout and not the actual construction
of a panel, but the following may help even if it is a bit of a thread fork.

The 300 (along with all single seat DGs) uses a molded fiberglass panel
which is also the primary structural element of the instrument pod. It
might be possible to fold up an aluminum sheet replacement, but that
probably can't be done right with home shop tools. It is likely cheaper
and easier to buy a new blank panel from AMS.

Back to the original topic: there are two standard layouts that people
have used, both have three 80mm instruments across the top. The early
choice (from the days when most instruments were 80mm) was two 57mm
holes in the second row (one of which is missing on the OPs glider) with
an 80mm hole centered below. Later on, most people put four 57mm holes
in two rows in the lower part of the panel. You can put an additional
57mm+ instrument in the pedestal that supports the instrument pod, this
is where the radio usually goes, along with fuses, power switches, etc.

It is pretty difficult to come up with workable alternative arrangements
(although you can obviously omit holes), as there are various clearance
issues with the pod cover. You may also run into troubles with long
57mm instruments in the lower part of the panel, I couldn't get a B50 to
fit properly down there, and (while I haven't tried it) to get a 302 to
fit you may need to take the cover off the serial cable connector. I've
seen some ugly looking mods to the cover to allow for alternative
arrangements and deeper instruments, don't go there if you don't have
to. If I can find a picture of my 303 panel (latter arrangement above,
with compass in panel), I'll post a link...

Marc