I have two 71 nova's and I would like to install big blocks at least one of them. what I would like to know is are the heater boxes on the inside of the car different? I know the outsides are as well as the heater core. I installed a 355ci in oct and since then I keep breaking heater cores when I give it the gas. I have all ready install polyuhrane engine and trans mounts incase that was the problem. it looks like the I need to move the engine forward to get it to clear. but I didn't have this problem with the old 350ci. Any pics or help would be great!