Many thanks Ian.

I'm really up to ordering some Ilford HP5+ 9x12 sheets in order to get some LF negs out of it which I will use for contact prints.

The green glass is a plate, ruined by now

You need film inserts to convert the plate holders although a piece of black card will work.

Just replace the glass with a card and put the film on it? The card must have some thickness to have the springs underneath pushed down I presume. Anything other special to have light leaks countered?

The I is instant whatever shutter speed is set, the B is bulb, shutters open while the shutter release is depreseed (or cable realease) T is time, forts press opens the shutter, the second closes - usually used for focussing, or like B long exposures. (ZDM is the same but German symbols). DF is because the shutters made by Friedrich Deckel who also part owned Linhof.

I assumed the above by playing with the shutter a bit.