mounting

So I snagged a Samsung 70 inch NU6070 grreat. I take down our 55 inch that's already mounted (the mount is universal VESA and handles up to 110 lbs, the new TV is only 58 lbs) to put the brackets on the back of the TV. Wrong screw size. I look in the book. It says there I need 49 mm, M8 1.25...

I have a pre-installed tilt/arm with a flat, non-removable panel that has 200mm x 200mm VESA holes. My new 43-inch TV has 100mm x 100mm holes. I see adapters on Amazon that can upside a small arm/panel to fit wider holes. But I can't find any conversion/adapter to get this 100mm holed-TV onto...

I'm not sure if this would even work, pretty much you would take your average TV mounting bracket and install it on the wall sideways, and then mount the TV to it like this (prepare for paint drawing that was made in like 30 seconds just to try and make my point clearer) would this work or...