I may be wrong about this, but I don't think Brian Wilson used electronic choruses at all. I think what you hear is multiple highly-complementary voices mixed acoustically into a single omnidirectional microphone. Very hard to duplicate, so congrats in advance if you pull it off!
One of my favorite references for that kind of thick BGV is "Little Lies" by Fleetwood Mac. No choruses or other electronic help on that one, either, except for the ubiquitous Lexicons. Another, of course, is Bohemian Rhapsody. These two examples may seem to have little in common, but the way they were recorded was the same: multiple passes of multiple simultaneous voices.