If a Header is properly/purposely built for a B16A it will NOT clear any other Block besides an B16A Block.
Proper length/clearance means it will touch when installed on a taller block.
At the Very most MAYBE a B18/B20 Non-VTEC Block which is very slightly shorter than a B16B/B18C.
B16A: 203.25mm
B18/B20 Non-V: 211.84mm
B16B/B18C: 212.39mm
The differences may not seem like much but when it's a close fit every mm counts.