Top end apart. Couple pictures couple questions.

My head gasket was leaking and I had a replacement gasket set on hand so I tore into my motor today. I haven't done this before but I bought this old bike to learn.

Here the valve cover is off:


Next the head is off:


Here's the head itself


Right now I'm trying to get the cylinders themselves off and they won't budge. I was thinking I should replace the base gasket since I'm this far in. And now I'm pretty sure I have to because I've been whacking them around so much. I tried to stick a screwdriver in the groove on the bottom and pry it up. Oops, put a small chip in it:


Here's the top of one of the pistons. They both look the same with all sorts of deposits:


My questions for you gurus are:
-Any suggestions for getting the cylinders off?
-Neither the head gasket nor the valve cover had any type of o-rings even though the manual said they should. Is this something meant for the 400 motor or should I have o-rings in there? The gasket set does not include any.
-I have some valve seals. How hard is it to replace these? I want to do this while it's apart but am a little intimidated by it. I'm using an online manual until mine comes in the mail which doesn't say much about it.
-What are those deposits on the piston and is that normal? What is the best way to clean this up?

Sorry my camera sucks so bad.

Thanks.

Brett

Should be able to cut a small block out of two by four and lightly tap around the block, try to find a place on the block where your not hitting fins. It takes time, just keep taping around on it, also there maybe small indentions, pry points between the engine cases and block, be very careful but if you have a large screw driver lightly tap, do not try and drive the screw driver into the two, as for the valve seals, a large socket stuffed with news paper, and a quick rap from a hammer will get the keepers off, make sure your socket is roughly the same size in circumference as the valve springs. I use a homemade valve spring compressor to put the keepers back on when i am done, Its a large C clamp with a piece of pipe cut out on both sides.

Looks to me like the pry point is right where I drew the yellow arrow. MAKE SURE there are not bolts holding the block to the top case before you pry or beat on it. Put a large screw driver in that pry point and gently rock the block. Don't beat on it with anything if you don't have to.

If all the bolts are out, the block should come loose from prying it gently.

Service manual is here Service Manuals

A proper valve spring compressor is about $30 on Ebay. Why fool around with make shift tools?