I put a big block in my 99 Camaro. It has been so long I can't remember if I had to move my engine over just slightly for the tranny to fit. I did push it back as far as it could go with minor firewall adjustment. I also had to notch the floor a little for the linkage to work right in a powerglide.
Good luck with your project the headers are a pain in the *** to make for a big block conversion.