i have a 71 240z and was running into a similar problem, my car never died on me (knock on wood) but the smell and a lot of smoke as a factor. nevertheless, i would have someone (if you dont know how) tune the carbs and make sure the timing is right. the carbs are probably the issue, you want to make sure the mixture is correct. i see youre in fresno, im in soCal so i dont really know anyone up there, but i guarantee there is someone in hybridz up there. get yourself the manual, try yourself, these cars are awesome and the stock motor is easy to work with. if i were you, i would keep the 260 block, get yourself a p90 head and swith the carbs to early Z (70-71) carbs, unless money is not a factor, get yourself some Webers. Also, i would recommend getting an electronic distributor if you dont have one. good luck!!