The Healey Restoration Guide (Anderson/Moment) also suggets that "the first hoods installed on the BN4 had an internal brace welded across the rear at the hinge points, but did not have a brace across the front of the hood, and had a styling crease running from then grille opening to the rear of the hood..."
So if your hood doesn't have a brace across the front of the hood, it is likely a replacement hood from a '57 or '58 model
The Guide goes on to say that "Subsequently, hoods were produced with both braces but without the crease..."
Personally I like the crease, if originality is not an issue. They're quite rare, and you can always pick up a correct hood on eBay for a couple of hundred dollars.
On the other hand, why would you put a 100/6 grille on a 3000? Is the grille surround from a 100/6 as well, or just the grille itself?
Sounds like a "Bitsa" - bitsa this, bitsa that..
Cheers
DB