I've got two air return vent holes in my floor that I'm patching, and I made the classic mistake of mis-measuring the flooring (the guy at the flooring store did, too, so I don't feel too bad) before purchasing a small bundle of 3/4" solid oak flooring planks (tongue & groove). Come to find out, our flooring (1951 home; it's the original flooring) is actually 7/8" thick, not 3/4". I was more than a little surprised to find that 7/8" thickness was even a thing... I've seen 1" thick stuff before, but only in novelty situations like This Old House episodes. Searching online doesn't seem to give any results for 7/8" thick flooring of any kind... I've only found one website that even mentions it as a possible thickness.
Even if I used two layers of felt underlayment, the new flooring would still sit below the height of the existing flooring, and if we stick with what we've got, we'll likely have to cut off the tongues and bottom groove of each new piece to even fit it in, let alone get it to sit flush/level with the existing flooring. I certainly don't want to sand down ~1/8" of the old floor of an entire room just to get it to sit level with two 2sqft patches...
The current idea (I've thought through several) is gluing 1/8" strips of wood to the bottom of each piece after it's been cut to length, and the tongue & bottom groove cut away as well, so that each board can be placed in flush with the existing flooring.
Is this matching project possible/feasible? Or should I just try to find 7/8" solid red oak T&G flooring somewhere?
Here are some photos for comparison; Old flooring:
Unfortunately I don't have any closets or inconspicuous areas I could steal old flooring from to patch these holes with matching/original stuff.