you're mistaken on the power vs weight being why buicks are fast
most turbo regals are raced are at 3600-3800lbs
the torque on the little v6 turbo makes them quick out of the hole
as to hp
the v6 can make anywhere from the low of 50hp (nearly stock 86-87 gn with a chip and some boost) to 100hp per cylinder (turbo heads cam good fuel improved air in and out) stroke and gain a little more, move to a stage or ta platform with 270+ cubes that will survive and 175-200+ hp per cylinder is possible and those are real rear wheel numbers on the hp
but do what we do but to a v8 and youll have more hp
as to the v6 engine being lighter its lighter than a cast iron v8 and definitely lighter than the bigblock iron motor but have you weighted an lsx , about the same weight as our v6 and lots of potential