Yours is probably OK to use as-is. This is a common place for them to crack, it is not in a area where high pressure is found.
Which head would be better for me, the high dollar 6/1 or the 5.5/1
Snyder's charges the same for both the 5.5 and 6.0.
I originally bought the Snyders 5.5 head and installed it. I was so impressed with the performance, better hill climbing, faster pickup, that I sold it and installed the Snyder 6.1.
I am very happy I changed it out. There was a noticeable difference from the 5.5 vs 6.1. Although not as noticeable a change as was the original 4.2 to 5.5 swap.
I can not imagine what a 7.1 head would be like. If someone made one that looked original i would go for it.