U are correct, it’ll fit the recess but to be perfect a bit of bedding/fill req to be perfect, vs a Rem 700 BDL cut out, you’ll need to hog out.
Now Hawkins makes a BDL style piece that fits the M5 cut and works great, but if your looking at an old school look in your build..bout only choice left n with Badger no longer making n PTG not making replicas, you might find a heavy duty version with Sunny Hill or an older Williams piece…