Here are my back of an envelope calculations using just your "very realistic" rents:
Rent $250 x 22 lots x 12 months = $66,000 gross income x .6 (assuming 40% expense ratio) = $39,600 NOI / 10% cap rate = $396,000 market value.
$396k - $275K = $235,000 gain.
That is a nice piece of change, but you will need to move in and sell 16 homes which might take a pretty long time and something like a $240,000 capital outlay. I guess with a park that small, all your profits are in the last few homes. That is to say the homes you have in there now will just be covering the fixed (and nearly fixed) expenses. So you will need some deep pockets to pull it off and not get in a tight place when the loan balloons.
Others can tell you better then me, if you would be better off waiting to sell after all the notes on the homes you sell have paid off (and you have your $240k back) or if you could go ahead and sell without having to discount the notes too much.
Also, I would guess that when it is your time to be the seller, you will have to play the bank just like the current owner is. Hopefully some other forum members will school me on selling a small park like this and tell us from their experience that, yes indeed, banks will be happy to loan on a full 22 lot park. That would be great.
How do I see it, going off half cocked; Don't consider it if you don't have $300k kicking around that you don't mind tiring up for a number of years. And if you do have that kind of spare change, why not look at a bigger and better deal?