Several things come to mind. Why are the manifolds cracked - overheating or worn out? You could weld them. JB Weld works if it does not get too hot and does not have high pressure. If they overheated then what else is damaged. Is your water pump bad, etc.
I looked at the boats and could see one that looked like it had Barr manifolds and the other was interesting and I wonder if it is a closed system ( the coolant stays in a loop with a heat exchanger ). No need to drain the blocks in the winter and not much risk of overheating. I am not familiar with those newer designs. I would go to the original design assuming it is a closed loop system. I have the older V6 with the log manifolds which are fine but it is hard to get to the petcocks to drain the block and that assumes you remember to drain it before the first hard freeze cause they surely will freeze and crack if you give them half a chance. I do not recall seeing much on ebay about CrisCraft manifold parts but I peruse the OMC list. You need to get a parts manual for your boat (easier said than done)to get some idea of the way it is put together from the schematic and to get some part numbers so you can call some of the dealers looking for the parts. You might gather some information from someone on a dealer call. I deal mostly with SeaWay out of Seattle but there are plenty others out there like Crowley. I bet whatever cris craft did was an improvement over the previous design and I would try and stay true to it. Hope this helps. TK