http://fiveoneoh.com/tech/roper_ka.htm
Theres a good site for you to check out.
Your altima engine will not suited for this, as it is fwd format, the block is different. It does have some good usable parts for hybriding and such.
You will need a ka and transmission in rwd form (2wd hardbody, 240sx). Ka24e and Ka24de are both options. That article above will be helpful.
Thats for a 510, but 1200, roadster, etc... have all been done semi-easily as well.
There is a dcoe/mikuni phh type carb manifold available for the ka24e, courtesy nissan carries it.
With the de you will be doing some custom manifold fabrication to run sidedraft carbs. Although you could run a v8 4bbl type carb with a truck intake manifold, has been done a few times.
I think you should keep with your megasquirt idea, and keep either engine efi. megasquirt is my management of choice
