GenI or GenII

I am planning to replace my Aussie 308 with a SBC. I love the look of the 'Front Running" serpentine belt system but am told that this only fits a GENI and not the GenII that I was planning on getting. Can anyone tell me of the diffferences between the GenI and II. I wanted a single rear main seal and roller followers and am not sure if the GenI has these features.

gen 1 has a 2 peice rear main seal and non roller lifters, but can be converted. Gen 2 is a 1 peice rear main. Not sure if there all roller rockers or not.