Merbesfield,
There are deep 6's and flat 6's.
The deep 6's were produced from 1969 to (I believe) 1972. The deep 6's with hearts being made in 1969 and 1970 only. They have a deeper lip and they look wider than the flat 6's.
The deep 6's are harder to find and more valuable.
Here is an Ebay ad with 2 deep 6's and 2 flat 6's. Very good pictures.
6x15 Polished Fuchs For Sale (2 are deep 6's w/ hearts) : eBay Motors (item 300394218261 end time Feb-15-10 19:38:57 PST)
Randal