You will be able to drive it depending on if you put an aggressive cam in the motor, and change the injectors.

Best way to approach the situation would be to do whatever you plan with the motor, and change the injectors at the dyno before your tuning begins.

If you are more concerned with extra cubes just buy a running 5.3 and build your 4.8 when the funds allow. A stock 5.3 will have more CI then putting 5.7L slugs in your 4.8

And as a bonus you can use the 5.3 rotating assembly when the 4.8 gets bored and you will have a true iron LS1

 

Are E85 injectors a bolt on upgrade? My truck is a stock '05 and I run across used sets of E85 injectors pretty often so they would be an obvious choice for me.

 

No, They use a different pigtail. You would have to get adapters or cut and splice your harness for the correct pigtail.