Not to rain on the idea too much, but ...
So, to end confusion, we go from 15 forums to 25 forums while dropping all of the General Discussion forums? How many threads would the 15000 - More lamps / clocks forum have in a year's time?
Ford's system is essentially an accounting system adapted to inventory control. It works for its intended purpose of keeping track of parts. It doesn't work so well for a growing body of information about custom vehicle work.
Organizing the information has to consider the state it is in now as well as how it might grow. Using the fine-grained categories of an inventory control system at the beginning will increase the complexity while leaving many categories nearly empty or unused. It begins full-blown rather than growing with the information store. If it doesn't begin full-blown, then it leaves the same holes as the current system, where there are specifics without their parent containers.
Beginning with broad categories ensures that all incoming information fits somewhere recognizable as related to that information. It also allows for more specific categories to be added within those broad ones, as growth dictates, and makes it simpler to shuffle the more specific information from the broader, parent category into the more specific, child category.
Example: If suddenly super-poly-ultra-squirt-a-frame becomes all the rage and 5,000 people a day start posting questions about how to get the hump of their nearly finished 32 replica frame past the rollers in the inkjet, and how many cartridges does it take for a '34 Duesenberg SJ replica, there might need to be a 126.96.36.199. Structure - Squirt-A-Frame subcategory made. At least most of the sudden onslaught would land within the 1.1.1. Structure - Frame or Unit - Fuel storage parent forum, before the subcategory was made, anyway.
(The numbers are there only to outline the structure and see where things fit. They are not intended as part of the name of a forum).