I have no links, but I can share with you my logic. As I thought earlier, and hence my asking you, your system may be on the small size for your conditions.
For general sizing, calculations have to assume your Gallons Per Person Per Day, and that varies from 50-75 from all my reading. Your ACTUAL GPPPD can only be found by you if you have a meter somewhere in your system. I used 60 when doing my calculations; actual usage is ~44. But for the sake of getting your answer, let's assume 60 GPPPD.
At 25gpg of hardness, plus 2.5 times 5 to compensate for iron, that's 25 + 12.5 = 37.5gpg For simplicity, let's round that up to 38. So we need to soften 38gpg X 60GPPPD X 4ppl = 9,120 grains per day on average. Plus, you want to have an extra day's worth of capacity to allow you to reach 2 a.m. the next morning (typical setting is to regen at 2 a.m.), so we need to "save" 9,120 for that. So for your 64K system, if you use 8 lbs of salt per cu ft per regen, you will have an actual practical capacity (with new resin) of about 48,000 grains. If you multiply the 9,120 above times 4 days, you will need to overcome 36,480 grains of hardness; but don't forget to add the reserve, so now it's 45,600. Since your softener can accommodate 48,000 grains, and you only need 45,600, you should be ok, but it's close. So you will be regenerating every 4 days, using 16 lbs of salt per regen, or about 1,460 lbs of salt per year. At $4.25 per bag, that's about $155 in salt.
I hope this helps, and best of luck getting your system working again!