Got them off, dad's friend said to use a stiff putty knife. We hit the gasket away at the top enough to get a screwdriver in between to pry it up. Thanks- Caleb  

The only reason people will tell you to choose the 350 over the 400 is the simple fact that it is a much more well known engine and performance parts are easier to find. The 400 is larger by almost 1 liter (.9 L) then the 350 and can produce more HP and torque. I own a 400 and I love it, its the best engine ive ever had in a car. So its basically a matter of personal opinion, but I would choose the 400 10 out of 10 times over the 350.  

Nothing wrong with the 400, overheating issues almost ALWAYs are the result of poor cooling system maintenance. If you compare your 400 Cyl. heads to a 350 or smaller Cyl. head, you'll see there's an extra set of holes in the deck surfaces of the block and heads (between the cylinders). These holes prevent the formation of steam bubbles between the cylinders, and are only found on 400's because they are a siamised cylinder block (the cylinder bores connect inside the coolant passages inside the block) to allow for the bigger 400 cylinder bores. Any small block Chevy cylinder head can be used on a 400 block, as long as it has the extra holes drilled in it to match the block. The easiest way to do this is use the 400 head gasket as a teplate to mark the holes. When proper cooling system maintenance isn't performed (Personally, I flush and change coolant twice a year in all my cars, early summer and late fall), the rust and sludge builds up in these steam relief holes and plugs them up (Their only about 1/8 inch). Was your 400 running before you got it? Later 400's are known for thinner castings, that are more susceptable to cracking. I would use one of the casting number decoders to find out what year block it is, and if it's after about 1975, it would be money well spent to have it checked for cracks before spending any money on rebuilding / assembling it.