I have a 1977 L48 SBC that I don't know much about as it was swapped into my 1984 bird before I bought it. Owner who did the swap has unfortunately passed so I have no additional info other than the son told me the block was decked (haven't opened it up to see if pistons were bored) and it has an aftermarket cam in it. I have tried both directions of mechanical water pumps, replaced the radiator cap, added cooling additives, installed new hoses, etc. I have installed a new radiator and a dual electric fan that is running air the correct way through the radiator. Thermostat opens properly. Car stays at ~190 when going above 30 mph, but once it's in traffic, it quickly shoots up to 230+. Gauge is hooked into the intake manifold and not the block. Thought I had the timing pretty dialed in as she's running pretty smooth, but I have read that the timing being slightly off, or a rich air-fuel mixture could cause this issue.

Any help would be greatly appreciated as I'm at a loss on how to continue tackling this issue.

Are you going only by the factory gauge on the instrument panel? if so, they are notoriously inaccurate. Unless you're seeing evidence of actual overheating, get yourself an inexpensive infrared temp gun and check engine temp with that.

I have a mechanical temp gauge installed on the intake. When it gets up to 230 and I park it, I can hear water boiling/sizzling out of the hose hookup.

Fix the leeeeeeks FIRST.

In factory single-electric-fan cars such as mine (83 L69 Z28), the fan switch DOESN'T EVEN TURN THE FAN ON until 234°. Meaning, in the factory's opinion (not that they know a damn thing about cars, butt w/e) the engine doesn't need cooling until AT LEAST that temp. If it sits and idles in 100° heat, the temp will climb to about that, the fan will come on, it'll cool down to 210° or so, and the fan will turn back off. The temp will begin to rise again until the fan comes on. It will sit there and do that until it runs out of gas.

A 50/50 mix of water and antifreeze at 16 psi boils at around 265 - 270°.

I'm not seeing where there's anything wrong with your car, other than the leeeeeks, and maybe not using proper coolant, based on your description. Certainly not "overheating". 230° IS NOT, in and of itself, "overheating".

84, with V-belts turning the pump the same way as the crank, should use the pre-88 pump. Later ones with a serpentine belt turn the pump the opposite way. Eeeeeeeezzzzy enough to tell; if the BACK of the belt goes around the pulley, it's a backwards one. Otherwise it's the old style clockwise type.

I should've elaborated more in my original post. The coolant doesn't leak until I turn the car off and the coolant is no longer cycling. I try to keep it under 230 with the fans and running the heat, but it has climbed to 250 on a nice 70-degree day when I was stuck in traffic. I shouldn't say the coolant is boiling as much as its sizzling when it hits the intake manifold which makes sense since it's in open air on a hot surface.

^That tells the story, right there. You need more fan, or fans coming on earlier. If it gets up to 250, I'd say your fans aren't working at all, or they're woefully inadequate for your combo.
But whe 30 mph = 190 (you have air flow), and "in traffic" = 250....that's an air flow problem. What creates air flow at low speed? The fan(s) do. Or they should.

I've currently got dual fans from a camaro in there right now, they are hard wired to a switch in the dash so I can have control over them. Ill look into seeing whats available.

Thanks!

Make sure you have an airdam.

His problem is NOT, at speed....it's while moving slowly or stopped. Air damn ain't the problem. Fans are.

Like Sofa said, if you've got coolant hitting the intake manifold, Fix the leeeeeeek that's causing this. Whether your seeing it while it's running or not, it's not normal either way to have coolant sizzling on the manifold