I have rigged 20's with twin motors before, but they were the 165 lb Mercury 65 and 70 hp 2 strokes, and the 182 lb Evinrude 70 hp 2 strokes. Modern 4S motors are way too heavy for twins unless you drop down to the 50-60 hp range, where you can get started at 205 lbs.
I used to have a 2 hp Suzuki DT2 as a kicker on my 20 Seafari, and it would push me along at about 3.1-3.2 mph on the gps at WOT. Back it off to 3/4 throttle, and I still got 2.5-2.6 mph. So you don't need a lot of power for a kicker. On the other hand, when I had a Chrysler 9.9 hanging off the back, I could troll at 6-7 mph at 3/4 throttle, but full throttle only netted an additional 1.5 mph.
I recommend a reliable 90-140 hp single OB, AND a small 3-5 hp kicker, plus Sea Tow or Vessel Assist/TowBoat US, plus a satellite phone, in that order.
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Common Sense is learning from your mistakes. Wisdom is learning from the other guy's mistakes.
Fr. Frank says:
Jesus liked fishing, too. He even walked on water to get to the boat!
Currently without a SeaCraft 
(2) Pompano 12' fishing kayaks
'73 Cobia 18' prototype "Casting Skiff", 70hp Mercury
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