most of the issues you will have will arise because of the Olds conversion, as the only short block difference between a Buick 350ci and 340ci is the bore size.
however, the valve order on a 350 is different from all previous gens of the small block Buick family so cam, heads and intake are not compatible with previous years.
the "SP" code engine from 1970 was the highest OEM hp rating that any Buick small block ever had and part of that comes from the one year only shallow dish pistons.
the Le Sabre is a longer car so you'll probably need to use your existing drive shaft or have a custom one made.
The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
Government schooling is about "the perfect organization of the hive."
H.H. Goddard, Human Efficiency (1920)