Since you are trading a studio and OP and MC (MSE) have studio units, II will automatically match you to a studio at these resorts (you
can't request only 1 BR) if one becomes available. And the studios DO become available much more often than the 1 BR's. You can put in the request for Custom House because they are ALL 1 BR - I don't know how good your chances are there, it is their high season. (I DID see one in flexchange a few weeks ago.)
There is a possibility of getting them, though, as I have seen many of both in Flexchange this summer.
You have a couple of options with this.
You can put in ongoing request, but monitor your II account daily. If they confirm you into a studio, call within the 24 hrs. and cancel that. Continue until confirmed into a 1 BR.
Or confirm into a studio and take your chances of upgrading during flexchange. To do this, you will need another similar unit to search with and it will cost an additional $99 exchange fee, but with the Marriott priority, I have seen LOTS of 1 AND 2 BR at both those resorts during flexchange this summer. In fact, OP had a 2 BR OCEANFRONT this morning that I could've picked up with my studio. Unfortunately (?) I'm going to HHI that same early August week. Can't be in 2 places at once.
