The only way to have unsigned code on a 360 is to have one with the SMC hack (aka JTAG hack and the earlier iteration of it known as the king kong hack) which MS blocked back in August 2009 or to have a developers system.
I think all the XBLA glitches have been negated (whether proper profile sharing rather than the anonymised method people were using is still viable or not I do not know) and XBLA has a few emulated games among the ranks but occasionally XBLA collections make it to disc so you might get something done there.
If you do want emulation grab an original xbox as the consoles you mentioned have top notch emulation there (certainly better than the 360 N64 emulation although not as nice as the PC stuff).
