What would you do?

Not sure if it helps or not but, I had a noisy lifter problem on my 318 with new j-heads until I upgraded to a 360 witht the same heads, (installed new springs). I went with the comp 901-16. The interesting thing is that 6 months before rebuilding the engine I had the heads rebuilt. New stainless valves, Viton posi seals,new springs, mild porting. I also went to adjustable rockers at that time too. I thought my issues were with the "new" j-heads.
When I pulled the springs off and compared them to the new ones they were almost 3/4" taller than the comps....not sure what they were and never asked the shop. I had similar issues as you. lifters were good first 20 minutes,(Once the engine got nice and warm) not so noisy at low rpm, but got worse with rpm"s. I am convinced it was because of the taller springs having to much pressure. They were a real ***** to compress and get the locks out. All the old lifters looked good though, no unusual wear patterns or such, the old cam did look like it had more wear than normal though.