Keep in mind that the G3 itself was rare, I think only five or seven were built, mainly for the Reading's Intercity trains, the Wall Street, the Crusader, the King Coal and the Schuylkill. They were also used on the Queen of the Valley, between Jersey City and Harrisburg, and only for about five years. Then they went to the PRSL where they were used on the Cape May Branch for a few summers.
The G2 Concor imported was part of the original 1937 Crusader train. It was accurate to the best of my knowledge, but I declined, and couldn't get one without buying the Steam loco. (It would have looked great behind a pair of FP7s).
If you're interested in Philly commuter service, before electrification or the Newtown Branch, then Camelbacks are in order. You will have a problem with 15" or 18" radius curves, unless you use shorty coaches with talgo type trucks. Bethlehem Car Works sells decent accurate kits of Reading and CNJ passenger cars, and between the other manufacturers, you can buy Reading suitable diesels to go with them, all for substantially less than a brass G3 would cost you, assuming you can find one. But they run better on 24" radius curves or better.
BLI imports T-1 4-8-4s built from 2-8-0s during the same time frame. They were used on the Famous Iron horse Rambles, after being retired from regular service. They are quite common and go for reasonable prices.
Good luck on your search.