engine and tranny drop

I was wondering if there were any larger engines that would drop easily into a mid 70's datsun 280z? (v6 still tho) Also are there any 6 speed trannys out there that match the 280's engine? Or are there any that can be easily modifyed? If there isn't any larger engines that can be installed, what do I need to go through with to port bore and polish the engine block? Like whos the manufacturer of performance heads, camshafts, valve stuff, ect...