well.... i did this exact same swap. my 77 nova has been 383 stroker, 355 nitrous, 355 turbo, 355 w/ a D3r, and now 481 BBC(supposed to run nitrous but out of funds). and what i did was a becool aluminum radiator from summit, and the biggest thing that helped with mine was the dual electric fans on a switch. you can literally watch the temp drop as soon as u turn them on. can watch it from from op temp down to 100 degrees and it will still keep trying to go cooler. gotta turn it on and off. nice to see other people doing the same project.
mine started as a v6 3 on the tree. this is what it looks like now:
if ya got any questions feel free. ive been through it all with this car.