Paul:I agree with you on this. Those dual springs are not only stronger than need be, but the guides would have to be machined so the inner spring would even go on. I am running springs that are 93# on the seat and about 250# open, with a much more aggressive cam than the Isky 260. More aggressive cams require more spring pressure because they tend to "throw" the lifter off the top of the lobe, also they usually mean the engine is run at a higher rpm. I have had my engine to 6500 many times with these springs without valve float. The stronger the spring, the higher the rate of cam and lifter wear.
John