360,340 or 5.7 Hemi?

I would like some input and info. I have a 68 Barracuda notchback with no engine. I have picked up a newer K-member from a 73 Dart and plan on using it. It is currenly set up for a manual trany and I plan on keeping that. The question is since I need an engine should I use the 360 I have (after rebuilding it) and should I use a single 4 or a six pack set-up on it? OR should I get a 340 and go with a six pack.
OR get crazy and get a newer 5.7l Hemi and drop it in? If I go with the Hemi how much problems am I looking at to get it in? Can I still use the K-member or will I be required to change that? I know I'll have to change wireing but that isn't a big deal. What possible issues will I need to address??????
I'm leaning toword an "old school" set-up and using a 340 or 360 six pack but would like others input. Thanks