I use the same coolant filters and bases. What a difference.
You definitely need to drain your lower block. You might be amazed.
One of the 454's in my SeaRay boat had a minor coolant leak. Come to find out, the block drains were missing. The only thing holding coolant in was the dirt in the bottom of the block. I had to use a screwdriver to bust through the hard garbage, and then all sorts of mess came out into my bilge.
Engine runs much better since getting that garbage out.