Re: Factory fuel injection from a 97 chevy truck.
This systems are not really worth it and I doubt anyone has a high performance version. They are really an in between a throttle body and port fuel injection. They have a spider system in the manifold that doesn't age well and is basically a POS. I had a 97 GMC and while it was an ok system for a 1/2 truck, it wasn't something you were going to make a performance system out of. Besides those manifolds are set up for Vortec Heads, which is a different intake bolt pattern than a older style SBC.
If you really want to go with fuel injection and are looking to keep costs down, I would go grab either a TPI or LT1 motor from a Gen III or Gen IV Camaro. They will be cheaper to install in an '81 because they are a Gen I small block as opposed to the LS style engines. You can also look at an aftermarket system like what either Holley, Edelbrock, and some other sell. The cost is initially higher but is probably a better deal for you in the long run.
You could also go to LS1Tech.com and check out there hybrid and conversion section. They have alot folks stuffing LS motors into anything with four wheels. Now that the motors have been around since 1997 the junk yard prices have come down quite a bit.