$1700 for the whole motor? Good deal.
Go for it. Don't know about the NOS upgrade but in order to have your car breathe better you're going to need to buy the SVO/FRPP heads or the 99 PI heads and look into their intake.
If you choose to purchase heads. Save and go the extra mile and get them ported and polished.
Down time shouldn't be a major factor if some else is doing it for him.