Here is another model of an 8-axle heavy duty flatcar with a 45 foot long deck. This model is very similar to the 12-axle KRL 304 prototype flatcar. Overall length of the model is 15-1/8 inches. The model uses 4 pair of RailKing 2-axle Rollerbearing style sprung trucks.
Prototype KRL 304 12-axle flat car shown.
Here is a KRL 304 12-axle O scale model for comparison. This model has a 11-1/4 inch (45 scale feet) platform length and an overall length of 17 inches. The model uses RailKing 3-axle trucks.