Thats even more work than removing the transmission. Theres a lot of lines, linkages and wires that would have to come off to move the engine ahead at all. Even if you did the fan would hit the rad, then you'd have to take one of those off.
If your exhaust isnt brand new, or youre just lucky and hasnt rusted(yeah right), you'll probably end up buying a new system. Or atleast getting your cat. re-flanged.
It would be easier to drop the transmission than to move everything forward. I was in the same situation..."but what if I did this". Don't bother. Just drop the transmission.
Also, you'll need a lot of clearance to get the transmission out from under the truck, and more than a floor jack to move it. When I did it, lining it back up wasnt easy with a transmission jack, so I wouldn't bother trying with just a floor jack or something.
Take it to a high school and give them something to do. Theres nothing really hard, its just a lot of work.
But if you do decide to do it yourself...you'll need a huge extension or a lot of little ones to get to the top bolts on the transmission...
but remember...
....PUT THE TORQUE CONVERTER IN ALL THE WAY!
...one more
...
...change the front seal in the transmission while its out. These have a tendency to fail also, so change it and buy yourself some time while you can.