Neat car. What shape are those end rectangular speaker on the underside, as in what shape holes? That could cause problem with stock sized speakers and their covers. You'll soon know if the 4 stud holes are still there to mount the covers through the speakers below.
Yes, you'll want some sort of thin board or metal plate to cover the middle speakers, wouldn't need much as the original is thin anyway. Possibly just a plate over the centre and a few self-tappers to secure, don't want it vibrating with tunes or driving.
Depending how far you want to go, or how badly cut up it is, you may want to replace the parcel tray itself with a used cut from an original car. This is what I have although yet to weld in. Previous owner added much larger speakers and I want original size. Also, with those speakers in your photo they've likely hacked up the jack holder brackets under the shelf, or made them unuseable. It's generally accepted that no one would ever use the original jack as it ruins your bumpers but like to have it for originality, so that may not be a huge factor anyway.
The holes in the parcel tray are not original, but same like the hidden look. Original had the speaker cutouts and mesh covers over the board. Some aftermarket speakers would require some extra clearance too if sticks out from speaker mount but still lower than stock covers.
Oh wait, you mean the current speaker holes once speakers removed in centre. I thought you meant the new boards that sometimes have perforated pinholes in speaker locations. You'd definitely be wanting a new board since all 4 of your speakers will ruin your current one, it isn't useable.
However, be aware that nearly all new boards are the wrong colour for camel tan and need to be recoloured to match interior. There always seems to be some variation in the shade of tan, even new, but they are often a long way off.
Not sure if you have a new board or just the one in pic?
