Only way in finding out is install the BBC and do a visual check.
if hoses fit, good to go.
If not, then buy a brass/copper BBC core, swap it in present heater, and drill with hole saw, two holes needed for nipples.
You can measure hole distance from a heater stud from inside core mounting to nipples.
An afternoon job.
Tip: when replacing core, remove the four nuts seen on engine side, inside cover from heater box to trans tunnel to seat to over the rocker with a plastic sheet. pull heater box on top of plastic, swap out core, and reinstall box. No need in disconnecting cables and resistor block connector, but simple enough for connector. Use sponge weatherstripping for sealing firewall.