Olds79, I am doing a similar swap. I am putting a 5.3 Vortec Engine with a 700R4 into a 51 Chevy Pickup. I am still planning on how to address the trans/torque converter issue like you are. I really don't know what the best option will be for me, as I currently don't even have a flex plate for my engine, I am starting from scratch. You had asked about elongating the holes, and if it weakened your drivetrain. TCI has a flexplate, TCI 399753 that is made of billet steel, and it looks like it has both bolt patterns for the LS1, and earlier generation small block. I guess you would still need the crank shaft spacer though. Just another option. There is also a writeup on another forum that addresses this problem. www.ls1tech.com/forums/showthread.php?t=639693
Let us know what you decide to do. Like I said, I am still studying my options.