Although the SpecCast F250's are excellent, they represent the Superduty (F-250 thru F-450) body style, not the F-150 Glen is looking for. Other than the 1:27 Maisto and a few el-cheapo smaller scale knock off's there are no F-150's available.
Arrowhead Aluminum Accessories makes both a conical and a bellows air bag kit. The easiest place to find them is on evilbay. Search for : arrowheadaccessories. There are one of each of the kits on there now, but the auctions end in 10min. They go for $6.00 + $1.00 s&h and are worth every penny.
Don't chop the 34! I think it looks killer with the channel and section but keeping the stock roof height! If you do chop the top I guess I will be forced to build the one in my collection channeled, sectioned and unchopped!
The only time I have ever seen anything similar was when I was building my John Deere Rockcrawler. I was trying to figure out what to use for the front suspension and decided to try to make air bags from synthetic fishing worms. After cutting a section of the worm to look like an air bag I put it in the box with the kit. The next time I opened the box the radiator looked like the roof of your hearse.
Here's a partial list of tires and their sizes available for off-road builders. This is not a complete list but it will give you an idea of whats out there.
From Left to Right:
Dunlop from Revell of Germany Unimog
Super Swamper Bogger from So Real Concepts (diecast)
Super Swamper TSL from Aoshima
Mickey Thompson Baja Claw from Revell (Tomb Raider Diecast)
BFG A/T from Revell (CSI H2 Diecast)
Bridgestone Desert Duler from Satco
Good Year M/T (origional tread design) from Maisto (diecast)
Bridgestone Mud Duler from Satco
Sizes:
Note: The tires from the Revell Diecasts do not have any sidewall markings.
Another tire available is the 49" Super Swamper Irok from So Real Concepts
Also, all of the Super Swamper tires are available through http://rpphobby.com/