My instructor made an X16 out of two Northstars apparently a few years back. Bolted two of them together with a custom oil pan...and worked I guess!

Yes, engines can be "modular"...99% of GM V6s are based off of the 350/5.7L or other V8s, the Ecotec is also just half a V8 too IIRC. Ford's V8s? 4.6 and 5.4 are almost identicle and parts are very quite interchangable...IIRC all heads and bottom ends and stuff are. Also, I believe Toyota's 5.0 V12 (Toyota Century, google it) the 1GR-FE is just 2 1JZs. These type of engines are MUCH prefered because of how easy and cheap they would be...if you made them interchangable with previous engines, thats a buttload of money to save.