I realize this is an old thread, but I just joined this forum and I feel I have something to add to this subject. Besides, this thread ended before the OP solved his trigger problem.
I had the same problem. Loved my new-to-me Lyman Deerstalker, but the trigger was too heavy.
After removing and examining the lock system, I discovered that the tiny spring that recesses in the little hole behind the trigger was so stout that I could hardly compress it with my fingers. I replaced it with a weaker spring from a ballpoint pen. This spring turned out to be so weak that the gun wouldn't cock.
So, digging around in a box of springs I had out in the garage, I came up with a slightly stronger "ballpoint" spring and it turned out to be perfect.
My rifle now has a very light, crisp trigger and I couldn't be happier.
By the way, before any hall monitors start blowing whistles at me, I did safety-check this setup by slapping and thumping the cocked rifle from all angles, trying to make the hammer fall without actually touching the trigger.
It didn't.