get the leak down detector and see how bad or if its leaking then you can see if its just the cases or the head also you can remove the radiator cap and look for bubbles, spliting the cases is not bad just takes a while to get it all out and apart. plan a day atlest and pos a weekend.even though the seal is new does not mean its good it could have got a piece of metal in it or just been old and and failed ..
I would remove the engine and what ever else you feel comfy with, and set it up for one of the pa guys to stop buy and over see or get a manual.. if you have it out and ready to go you should be able to hmmer it out in a couple hours, taking youre time and learning.have all the parts and seals there , EVERYONE, and then if you dont need it you can return it and get the money . but that is better than getting half way through and relizing you need one and the parts house is closed or the need to order it..
my .02