65 cuda 273 to 360 tranny hookup

I am about to swap my 273 for a 77 360, what type of changes might I encounter. Can I use my 360 torque converter 3500 or must I us the 273 converter 2500. I have the 360 flex plate. Is the spline diff? How well will the old (rebuilt) 904 handle the power diff. of the 360---350 to 400hp? Thanks gents