Your best bet might be to buy either an emulator from Moates or a DynamicEFI conversion and learn to tune it yourself. There are a few members here who have tuned Vortec engines and could give you a timing table that work fairly well. Then, you just need to work on the fuel. You can probably get about 75% of the way there without a wideband O2 sensor but eventually you have to install one to do the wide open throttle tuning.

But to begin with, you will first likely either need more fuel pressure or larger injectors to provide enough fuel for that engine. So you could swap in a TPI fuel pump and a new spring in the regulator to get the pressure up to around 16-18psi. You could try the spring first but it's doubtful the stock pump can keep up to the fuel demands at a higher pressure.