Hi Ray . . . welcome to the forums.
The use of 307 slugs in a 250 has been discussed quite a bit here in the past - though not much recently. The slugs are the same diameter as those from a 250 but are absent the characteristic I6 dish so they raise the compression ratio.
Given that your engine's bores are 'worn out' you are likely into a heavy over bore get them back to round and square to the deck.
Do you have a set of oversized 307's in hand? If not a custom built set from Ross or Venolia might be an easier option. The block can be bored to 'whatever' is needed to make it right and then the slugs can be forged to fit - complete with zero deck height.
regards,
stock49
