904 flex plate

Hi guys, Would it be alright to use the flex plate out of my 273 and put it on my 340 with a 360 cast crank. The motor has been internally balanced. I read on another site that you can't do that. Is it to week? Has anybody had any luck using a Alabama torque converter, they seem to be really cheap. Or do you get what you pay for, just like everything else. Bob