Two Jewells offered, one for bench without a safety 1.5 to about 3 oz. pull. One w/ safety, 1.5 oz. to 3.5 lb. pull. Midway says "Gunsmith installation" -- It's not a "drop in." The sear engagement needs to be set up. What's that all about? I can set up valve clearances, read a caliper, and run a machine lathe or milling machine. Can I install one of these triggers?