The Nova CAME with the 350 Buick just a few years later so it is a bolt in. The transmission will need to be a "BOP" (Buick Olds Pontiac) pattern which is different than Chevy. There were also transmission called "dual pattern" which had both BOP and Chevy. I put one of those myself in my 65 Buick Skylark.
The motor mounts are the same, I honestly think it is a simple bolt in with the tranny being the only thing you will need to rustle up.