i've flown and built several. my favorite was with the fox 19 as pictured on the box. that thing would turn 18k on an 8-4, as advertised, and was a great combo! they aren't around any more, but we have also used os 15's and 25's, asp 12's and the norvel 15 pulls them well, and very light! your magnum will be fine. I would go w/ an 8-4 on a stock magnum, but with your mods you know what works best on your particular engine! don't sweat the weight too much. it is fun to see how light you can get 'em, but they fly just fine stock. have fun!