I have a very clean 85 Tbird with the 5.0 and understand that it is rated at 140hp as stock.    

What are my best options for upgrading the performance and ECU? My goal is to restore her and have performance more fitting of the 5.0. Something I can show and still surprise Monte Carlo drivers. As a beginner I am concerned about potential pitfalls associated with upgrades & engine swaps. Thanks.

Since it's on the old Fox frame, a lot of the Mustang tricks and parts would work.  Any engine mods, rear end, exhaust, would all go on.  If you could, get a 5.0 roller block and go from there.  If it's a carb, you're ok.  If it's CFI, ditch it and go with EFI from an '87-93.  All the sensors and wiring harness would go in as would the computer from the '87-'93.   

She has throttle body injection... I was wondering what path to take with it or in place of it, and it definately sounds as if I will be looking for the EFI from the 87-93.

What is a "roller" block and where is the best place to find one? I have been looking at some crate motors & haven't noticed that term.

Is Ebay the best place to look or is there a reputable place to shop?

Thank you for your imput!

A roller block is one that has provisions for the roller lifters and the "spider" retainer.  The lifter bores are longer and there's holes tapped for the screws to hold the spider in place.  Only '85-'95 5.0 H.O. blocks are like this so yours may not be one.  You could get a retro-fit kit for yours if you want to use it.  A crate motor is usually a roller, especially if it's meant as a 5.0 replacement.  DSS has them and you can get one fully prepped.  Central Coast Mustang has a few left.  E Bay is a good place to find used and factory parts.  If you get an used block, have the mains and between the cylinder walls checked for cracks.  Check the mains for "cap walk" too.