Help IDing an American flyer set

We can help. The 300 was only used in three sets, the 490T, the 4601 and the 4603. None of these have the 3 car consist you listed. The main issue is the 635 crane car, it was not used with the 300 type engine.  Having the set box may help. There will be a box makers stamp on it in one or two places. Pictured below is an example. Some are dated some are not. The B number will be on the box but possibly in a separate location. This information can greatly narrow down what set you have. See the picture below.

For example, the the 490T set used a B2004 box and the 4601 set used used a B1017. 4603 was a passenger car set.

The picture just showed up.

We are in luck, box #B1130 was only used for one set, the 1948 4801A freight set. The set box you have is dated 1948. The contents of set #4801A are as follows:

Engine-302; consist 628, 633R, 630; track 12-702, 2-700, 14-693; 706 uncoupler, 690 track terminal.

The Gilbert catalogs are online at myflyertrains.net, you can see the set in the 1948 catalog, p19. The contents in your possession do not really match the set listing. There are no reported content variations that match what you have.

I looked through all the set content listings from 1947 through 1952, both cataloged and uncataloged. The 635 was only used in a few sets headed by either a Hudson or a Northern. There were no sets made that included both a 631 and a 635. This means one of those cars was purchased separately, likely the 635.

Looks like I fat fingered the keyboard.should be 625 not 635.

Ok, but it does not change anything. The consist you have and the set contents for that box do not match. The 625, I assume, is either a black or a silver Shell tank car. Are the coupler weights brass? 1948 coupler weights were brass. In 1949 through 1953 they were black. 1946 and 1947 did not have coupler weights.