If I'm not mistaken the piston to crank angle of the two engines differs. The buick motor is built on a 90* angle and the chevy motor on a 60* . This creates a situation where the chevy with any power adders wants to push the crank out through the oil pan.
No the 4.3 is a 350 with 2 cylinders lopped off for the most part and both are 90*. It is similar to a Buick since the crank has offset rod journals for even fire but thats where the similarities end.