With the oil warm I would try adjusting them as hydraulics.
If after a few minutes (time for them to bleed down) you crank it over and it spins over to fast, like there is no compression, then you can assume you have solids.
When you say they are spongy I think you can also assume they are hydraulic lifters with air in them. Hydraulic lifters that are properly filled with oil will also feel solid.
You may want to read more about hydraulic lifters on
MY BLOG. On another note, not all blocks are drilled to supply oil needed for hydraulic lifters. Just because someone may have installed hydraulic lifters in this engine does not mean they will work.
