Sounds to me like your going to need a large tube header anyways. (something i bet is not a 'off the shelf' choice for your chassis). Depending on how 'nasty' the motor is,, a 1-3/4" ,,,, 1-7/8" or even 2" stepped to 2-1/8" primaries might not be out of line.
I'm sure part of your issue is the Vic Jr heads are angle plug and the headers ordered for your chassis are intended for stock, straight plug heads????
I'm up against the same wall right now. I was running 1-5/8" Hooker Supercomps for a Nova with aftermarket angle plug heads on my last motor in the truck. Had to notch the frame to get them to clear. But they cleared the plugs.
I'm in the process of stepping things up and needed a much larger primary. Only ONE way I know of to do that.........
You order one of these. Then with your chop saw, a TIG, grinder, lots of gnashing of teeth, cussing, grinding, ordering some extra (replacement) 1-7/8" tube to fix the screw-up's,, you have a custom set of headers that FITS both the chassis AND the heads, and the copious amounts of exhaust flow a high HP high RPM small block makes
