25 initial sure sounds like alot. I'd set the initial in drive at idle speed with the E brake on using the vacuum gauge method. Then with that # in hand I'd shorten the slots to get 36 total (checked with vac adv capped). Then I'd toss the heavy spring with the long loop on one end & keep the OE light spring for a baseline & want to stay just under the pinging point at WOT up thru the gears on your hottest driest day. If it pings you can add a mr gasket or MP light spring where the heavy spring was (along with the OE spring of course) or can trim the "tips" of the weights. Then hookup/adj vac adv by driving at a steady high vacuum interstate cruise at or above the RPM where the slots are maxed out & want to stay just under the pinging point on your hottest/driest day & can solder strips of feeler gauge on the back side of the can on either side of the notch to limit the arms' travel into the can. Can file the notches (both sides) if more travel is needed then with a 3/32" allen wrench slow the curve onset till you are just under the pinging point in everyday driving under varied conditions on your hottest/driest day. bottom line stay as close to the pinging point within reason as you can and any pinging you can hear is WAY too much. To get you primed right now with a 3/32" allen wrench into the can nipple turn it 2 turns CCW & see if the medium throttle pinging you have goes away. Do each subsystem in order: initial/total/springs/vac adv (2 parts)