Unless you have some sort of deep emotional attachment to that engine for some reason (like a title with the engine serial number on it) it would be a good idea to find one without a crack. They're not really all that scarce, and the only effective way to do a good fix is to strip it down to bare bones and preheat- - -weld- - - -post heat- - - -and peen the welded crack to stress relieve the weld. Don't weld more than about a half inch at a time between peening operations.
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
Love your enemies and drive 'em nuts!