A BBC with a performance intake manifold and cleaner will not fit with a flat hood. I ran my 454 with a drop base cleaner with a Edelbrock performer and got away with a 2-1/2" Cowl hood.
This is what I have found on repop bumpers. Must be mis-drilled mounting holes. The RS nose is a repop too.
https://www.ebay.com/itm/265689872760?hash=item3ddc59b978:g:Gy4AAOSwXhFiVlAn