I ran a 400 block in my Vega. It was a 377 with 6 inch rods and 12 to 1 pistons. Never had a problem after I found a good block. The first one I found had a crack in the lifter valley. I'd recommend that you have it magna-fluxed to be sure it is good. The machinist I use said they tended to have more probems with cracks when compared to the other SBC. If you keep them filled with coolant, they will live. There is a little grinding required on the pan rail when you go with a longer rod. I think they are a pretty solid foundation for up to 700 hp. I later went with a 400 crank and it felt better at the bottom end from the additional torque.