OK, this isn't about an engine but I looked and saw nothing on the Body etc. threads and besides all the old timers hang out on this one

For too long I've faced the dreaded job of replacing a striker plate that was preventing a door from latching. Finally good weather and I got charged up to tackle the job.
I had adjusted one of these before and knew getting the hex head bolts out was going to be a challenge. Last time I was just loosening the Striker plate to make the latch operate properly. So I learned how fragile hex head bolts can be after being in place a few decades ! (why didn't they make Torx head bolts back then?)
I started off by peening the head of the bolts with a nail set, something I learned that helps close the metal around the hex wrench tightly so it won't wallow out the opening and make the wrench useless. That failed, the hex became rounded out on 3 bolts, only one came out.
I proceeded to drill out three bolts and pulled out an old bolt remover I had on hand.
In the process of doing this a friend came by with a nice kit (last pic) but I decided to try the old bit I had on hand so I wouldn't damage any of his beautiful pieces. It worked, whew!

I got a little off-center when drilling a few of the bolts, the pic shown is the better of the three. Look close and you can see the threads on one side are basically like a skeleton with no metal underneath.

Then I chased the threads in the threaded plate one hole at a time with a bolt tight in the mating hole to keep the plate from falling down, I believe they are floating ie. non-captive.
Are there two plates? or one? my duh!

So this is where I have to ask for sage advise, anyone having done this will know more than I do.
If I removed two bolts on a side the plate in the door jamb will fall down, right?
I really want to avoid having to remove the interior covering so how can I keep the plate in place while I remove the old Striker plate?
or am I just not going to succeed with this and I need to remove the MB Tex over the door jamb?
the piping around the edges looks really awful anyhow, this is a well-used '79 300TD.
TIA DDH

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!