The 4500 is not "new". The 4500 is actually Racor's original design and predates the 3550 by around a decade. There is also a CCV6000 and a CCV8000 and a special order CCV12000. In the opposite direction, there is a very small CCV1500 and the relatively small CCV3500.

The 3550-FRD- 02 was designed specifically for the 7.3L PSD and came to market mid 2002.

 

I am just going by what is on their website, they do not even mention a 3550 as far as I can tell.

Edit - I found one

 

No, Racor's website doesnt market this 10 year old limited application product any more. But if you want, I can photograph the sell sheets that Racor used to have on their website for this product. Both versions. And then I can photograph the materials from the 4500 release from many years prior to the 3500 and 3550.. I have no incentive to speculate about such a thing. I have followed these products since their inception, prior to them being available for sale.