Hi,
1. Not sure about the head gasket, wouldn't have thought there would be much difference. Someone here will have a much more definitive answer though.
2. You will need new head bolts as they rely on a predetermined stretching of the bolt to get the required uniform clamping pressure.
3. I believe the 6A block is the same height as a KR block so a standard KR cambelt should do the job - Don't forget to change the tensioner pully at the same time, could save you a lot of pain and wallet-ache.
How many miles has the head done? It may be an idea to change the Valve Stem Oil seals whiule the head is off - I wish I did when I put an ABF block on my KR. You will get these anyway if you get a head gasket set. I believe Elring are reputed as being quality gaskets - it's what I used on mine with no probs in 15 months

Hope this helps
Cheers