I visited Hillbank in January and from what I understand the SPF & CSX 289 cars are virtually the same other than minor cosmetic tweaks. The increased price tag for the SPF 289 roller vs its 427 counterpart reflects its "custom" chassis that mirrors the original car in most respects.
The 289 is a BEAUTIFUL car in person & would be my first choice if I could justify the 100K plus price for a non-CSX replica. Actually, I could but I don't think the wifey would.