Bell housiings are different as are throttle linkage,header pipe, radiator, shift linkage,front motor mount,clutch linkage, u-joints are bigger than the 6 too. Trannys are the same except for the u-joint yoke. Friend would have to custom make a front motor mount, move the radiator back 6-8" or make a weird looking shroud. IMO too much work. 323 8's are a really good engine. Is this a really nice or rare model of car? If it is and he likes it a lot he needs to properly rebuild the 8. The 8's do have exhaust manifold issues-they crack and are really expensive, they don't weld up well are hard to find as well as water pumps cost a lot of $$$$$. Straight 8 parts are just generally expensive. If the car is just a tired old 4 dr maybe he should move on. If it's a convertible or hardtop 1950 he needs to fix the 8.
Bob