Classic/Antique Car Repair: 350 HEADS, head gaskets, good shape

Question
I WAS TOLD THAT CHEVY 400 HEADS WOULD FIT 350 BLOCKS, IF SO HOW MUCH INCREASE IN HP WILL IT PRODUCE? AND WILL IT TAKE 350 GASKETS OR 400 GASKETS?  THANKS CM SIGMON

Answer
cmsigmon;
 Hi ,  yes  they will fit , use new 350 head gaskets , as far as h.p. +-5=10 %  it will run a bit better , but first off I would check the springs ,and rockers to be sure they are all in good shape. Check the lifters and push rods. If you take off the water pump and timing cover you can also throw a new cam in it , lol.