The LS stuff won't work with BBC or SBC. The 8.1L (same generation as the LS engines) has similar bore spacing and a couple other characteristics, but it's not the same block. You can't use the LS series setup without some type of reluctor wheel I don't believe, it's a different system than the older stuff. You may be able to use the 454 truck Vortec intake though, it's a port style injection setup. I'm not sure about hood clearance or what the port design is, though a quick look at intakes on Summit's site shows they're probably oval port.
It may seem like a step back, but you can run this with an EBL and OBD1 distributor (same as TBI 350, 305, etc.). The intake/injectors/throttle body don't know what they're giving the signal to/getting it from, so there won't be any issue running it. The other option is to simply run TBI, which involves an adapter plate for the throttle body, EFI distributor (NOT Vortec), and an ECM... this will be the cheapest route, but fuel can be more finely tuned with the port setup.
For TBI, you can figure $100-200 for the throttle body, harness probably $20-100 used depending on where you get it, EBL setup (with wideband O2 and ready-to-run ECM) $620, $20-50 for a distributor, $??? for your pressure regulator setup (there's a mod to the stock regulator or you can go aftermarket), and probably around $50 for the adapter plate.
For Vortec, add $20 to the EBL setup (for port injection), nix the TBI throttle body/adapter plate/regulator setup (-$100-300 roughly), and add probably $150-300 for the Vortec setup (throttle body, injectors, intake plenums, etc.).
It still won't be cheap, but it won't be the $3,000 you mentioned previously. There are ways to convert to coil-on-plug, and from what I understand you can even do it with the EBL using a Cadillac DIS system (similar to the 3800s of the day), and adding a reluctor ring + the sensors for it.