454 vs. 5.3 efi vs. 5.3 carbed

[bloodybigblock]

As my headline states.... I have an 86 c20 crew cab that has a great stock 454 motor with TH400 trans. Im unsure of the actual mpg in the rig because i need a new carb. I was also going to buy an intake,headers,and run an exhaust. By the time i do that, ive spent $800-900 in parts. I was thinking about swapping in the 5.3 motor and still retaining my TH400 trans because its reliable,tough,and i can afford a sturdy 4l80E. Is it worth saving the $800-900 and selling my 454 to purchase the 5.3 Motor? My parts list came out roughly the same price of keeping the 454 with those bolt ons, having a efi 5.3 with camaro manifolds and tuned with motor mounts etc, or having a carbed 5.3 with the msd box and edelbrock intake..................... so which one would be best for daily driving? I thinking hp numbers will be in favor of ls motor while torque being held by the big block. Im also trying to figure out mpg increase. Is there a bonus to this swap......opinions?suggestions? Thanks guys for any comments