""Okay, here are the numbers I found on the choke horn ..477B-7""

I think that your number may be 4778-7. If so than this is what I found:
4150 style, 700cfm, 69/78 jets, 6.5pv, .028 squirter.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)