The 1500XS 20" shaft was 275 lbs and the V200 20" shaft was 336 lbs. triples would be 825 lbs or 1008 lbs. And I know the V200 had a nasty tendency to self-destruct above 6500 rpm's.
Besides, you can easily fit triple XS motors on the transom of a 1973 20' Superfisherman. We had one with twin Merc 85 hp motors, and I commented at the time that you could fit 4 of them across if you wanted to. It would just submerge the transom. But not with a bracket
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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