I don't see the current 'core' lot as viable on its own if there's to be any preservation at all, it's only about 8,000ft2, and it's only ever going to get a mid-rise approval.
The lot out to the corner (917) looks like it may be under common ownership, but it's not legally the same lot.
Even then, you only get to a bit shy of 11,000ft2, viable as a clean site, but with preservation, I think the numbers would be hard to make work.
Now if you throw in 929, the lot the east, I think you have a very attractive assembly, enough so, that partial or full preservation might be workable.
That's in the range of 24,000ft2