SP1's are not any easier to conver than most any other semi-auto AR-15.
Colt stopped making them when they switched to the "Sporter II" series, and I don't know the exact reason for the model change in that case, but don't believe it was related to convertability, since the Sporter II is just about the same internally.
If you were to buy a full auto gun at a gunshow, you'd have 3 to 6 months waiting for the BATF background investigation and paperwork to go through before you could actually take possession - so you'd have plenty of time to go by the dealer's place and test fire the weapon.
Scarecrow: so cynical - how delightful. This is the colt forum, not the full auto forum - so there's no moderator to close/lock the thread. Further, while displaying ignorance, ardreamer's questions aren't designed to elicit conversion information - at least not yet.