Ah, an ext. cab.
As for the blower you should be able to find some of those Eatons at the National Lightning Owners Club website
www.nloc.net/ and also talk to the Lightning section at
www.f150online.com/ . Make sure you check out the Vendors section at NLOC. Many of the vendors there will have exhaust setups as well as other parts you want.
Also since you have the 5.4 Ext cab flairside you would be basically alot like the early model 99-01 Harley Davidson trucks so you should also check out the National Harley Truck Owners Club site at
http://www.nhtoc.com/forum/ . You could also probably find some Eatons from the 02-03 Harley trucks from some owners on there that are switching to the Kenne Bell's.
As for 4.10s they probably won't hurt your gas mileage all THAT much really. I would highly recommend 4.10s if it were my truck. That will help get that heavy truck moving quicker. I used to have a GEN 1 94 Lightning (came stock with 4.10s). We've had guys switch out to 3.55s and such and the mpg only varied by maybe 1-2 mpg. I imagine it's the same for the GEN 2 trucks.
Check with Bassani as far as exhaust goes. I believe they've got some setups for your truck. I don't know a WHOLE lot about the new model truck's exhaust systems but I have read about the Gibson not being all that great. Bassani definitely has better power numbers. Magnaflow is also a good one to use. They may not sell a specific catback for your truck but you can always get the muffler, which is straight flow thru like Bassani, and enlarge your pipes if you wanted to do so. You may even pick up an exhaust from a Harley Truck. I don't know if their exhaust is any different than yours except for maybe side exit.
Why would you not go with UD Pullies? Charging issues or something? I would think you might be able to make up for any mpg loss from switching to 4.10s if you run UD pullies. Something to think about.