I think the inlet manifold height might be the reason there are not many. A KR in a mk1 is virtually hitting the bonnet and I think the extra 15mm on an ABF would mean removing some of the cross-bracing at the very least. Also, it makes the exhaust manifold a bit more complicated due to the extra height.
The US never had the ABF so a lot of people make their own with a KR/PL/9A head onto an ABA tall block. However, I've just searched Vortex and haven't found one on a mk1 with the standard inlet manifold - only ITBs
