A few years ago, buildings 11, 12, 13, 14 and 23, 24, 25, 26 were made the separate booking category of "Hospitality House" so cannot be requested unless your reservation is actually in that category.
You should call DVC (1-800-800-9800) and explain your situation. Start by telling them it is an RCI trade; they can look up your reservation and note requests for you.
Probably you already know the following because you've stayed there before but, just in case...
The best building for the least walking will depend on whether you'll have a car or be using Disney transportation. If you'll be using Disney busses, your walk to a bus stop can be short even if you're not near the Hospitality House. For example, buildings 52, 53 or 27 are actually closer to a bus stop than 14. There are 5 bus stops at OKW so you can get to the HH from anywhere. I'll agree that being near the HH in the first place would be easiest.
We stayed in building 56 once and loved it because it had a quiet pool right behind and was close to a bus stop.
I see online that buildings 62, 63 and 64 are the only resort buildings with elevators - that may be important to you also.