The LGA115x/1200 backplate at least for Asetek-based AIOs work fine on LGA1700. Intel CPUs have those little sliders you just move into position. You can buy the LGA1700 compatibility kits for $5-10 but its really not necessary unless you want every last C and want to overclock to the max; the difference is maybe .5mm on the standoffs for a little more mounting pressure. I maybe picked up 1-2C using the official standoffs but it cooled my 12900K at stock just fine before that.If you're quoting Micro Center prices, why not the $350 12700K + Z690-PLUS D4 bundle? $100 cheaper, higher-end mobo, not that much farther behind in gaming in practice.
If the case can't fit a full-size ATX mobo, that may be reason to take your approach.
Also, while you can carry the DDR4 over, you probably can't carry over your CPU cooler unless you have LGA1700 mounting hardware, so budget for that too - perhaps one of those contact frames as well, to get around the IHS bending problem.
I also did the contact frame mod, just 3D printed it and it maybe helps 5C max.
If you want the best possible cooling however, you probably want to upgrade your AIO anyways at that point, I saw a much bigger difference going from my 5 year old EVGA CLC 280mm to the Corsair H115i Elite Capellix, but if my case could handle it I would recommend a 360mm rad AIO instead for another 5C or so.