That riveted-on plate must be unique to Canadian engines- - - -I don't think I've ever seen anything similar on a US-manufactured engine. Do the cylinder heads have the same number and arrangement of attaching bolts? If so, one option might be to swap the 235 head onto the 216, after doing whatever repairs or valve regrinding is necessary. Do both engines have a tall sheet metal side cover that goes up all the way to the valve cover? US-made spray oiler heads for 216's and 235's will interchange with no problems. Then you could work on repairing the cracked head and use it as you build up the 235 as a spare engine. There's somewhat of a learning curve involved in adjusting the rod bearing fit and oil clearance of a Babbit-rod engine. Good luck!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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