couple ways to do it from /6 to v-8

change the K-frame out to a v-8 one

use the conversion mounts

and if its old enuff /6 you can use a truck engine mount on the pass side and a stock v-8 bracket on the driver side when swaping from /6 to sb using the square bisket rubber mounts
(old hot rod trick)

a 350 is gonna need a torch and welder as it would be a chebby engine

a 383 would be the same set up as a 440 though,k-frame or conversion mounts

the tranny will bolt up in the stock location and use the tranny mount for that yr and style xmember

if going BB in an A-body the exhast is the biggest problem

and a 383 B engine is a little better fit as the 440 is wider at the valve coves and mucho tight on clearance

good luck