67 cuda upgrade... what do you guys suggest?

Last weekend I purchased a 67 Cuda (for wifey) with a /6 and 3 on the tree. My intentions is to fix the body first while she drives the /6. I only bought it with the understanding that I would later find a v8 for it.

What is the easiest conversion to a v8 when moving from a /6 manual 3sp?

Keep in mind I am still new to the game so I need it to not require too many modifications. I am thinking 318 or 360 but what do I do about the transmission issue???

Thanks
19dart71