The SP-101 is more of a known item to gunsmiths. Teddy Jacobson in Sugarland, TX does a lot of defense guns. Routinely most come out of his shop at about a 9 lb DA pull. I don't know what weight springs he uses in the SP's. As most are magnums they are a bit heavier sprung than need be to fire std. pistol primers. With the 9 lb mainspring in it and 8 lb trigger return be sure that the trigger reset is satisfactory and run a bunch of ammo through it that you plan on using. Mine must have had at least 800 rounds through it with the 9 lb mainspring but I put the 10 lb in just in case the spring were to take a bit of set. Another person that tunes defense guns is Grant Cunningham but he has a closed waiting list right now. They won't necessarily be as light as they could be made due to the intended use sort of like Teddy Jacobson.
Randy Lee of Apex Tactical gets really low DA pulls by lightening the hammers. He is primarily known for his S&Ws but has done Rugers in the past. In fact someone on one of the Ruger Forums has a GP in which he discussed the trigger. Using a custom lightened hammer
(Iowegan on one of the Ruger Forums showed where to lighten the hammer, see http://rugerforum.net/ruger-double-acti ... anges.html
) and perhaps a custom mainspring
I would think one might be able to get a bit under 8 lbs in double action if attention is devoted to firing pin protrusion
( http://rugerforum.net/gunsmithing/9965- ... usion.html
) and using std. .38 cal ammo.
Many run of the mill gunsmiths won't address some of these things (firing pin protrusion and hammer lightening ) in a tune up or action job. Might want to print out Iowegan's comments on the topics (he is a retired gunsmith) to show what you want done. That is one reason given what you desire I would be tempted to have Randy Lee work on it.