I am not a GM guru, but I would think that a 99 would be port injected? Seems late for TBI.
Either way, the major requirements are going to be the same- fuel pressure must be toned way down (most carbs want around 5-6psi), first off. You can switch to a mechanical pump or run a regulator. You'll of course want to accompany the carb with a fully-independent distributor; probably a 70's HEI. Mechanical and vacuum advance.
With the motor pretty much functioning on its own, it's then just down to rigging everything around it. Exhaust fitment, intake clearance, correct oil pan, ect. And whatever you're going to do about the PCM. You'll still need some selective functionality to get the car to start, I would think. Plus gauge functionality and all that.
I think it's legal to do that, so long as you keep catalytic converters on it. And the evap system, I guess...you could make it function if you really wanted. Though I highly doubt you'd ever be cited for it, you can get some big fines for any missing OEM emissions stuff. Whether fuel injection and computer control in general would fall under that, I dunno.
But more importantly, do you not have inspections and/or emissions testing where you are? 1996+ typically needs to pass OBD2 readiness. Pre-96 is usually a tailpipe sniffer.