This is similar to a failure a couple months ago on a 240. Similar symptoms, so you could have a similar problem.

It does sound like you've been through everything, though I may have missed it - did you say the cap and rotor are spotless?

Anyway, it's time to check the timing belt. These engines (I'm assuming standard non-turbo 740, Regina ignition, right?) will make spark and fuel but still not run, if the timing belt breaks or jumps time.

Set your crank to TDC (using timing mark on the belt pulley aligned to the long "O" line on the timing cover). Where's the cam sprocket mark? Should be within a hair of the tick mark at approximately 11:00. The pulley mark is a dot indented into a tooth. If it's off one or two teeth either way, there's your problem. If it's off 180°, turn the crank one revolution (doesn't matter direction) and align it again.

The problem seemed to be precipitated by a cracked timing cover, losing pieces from around the bolt hole sleeves down into the crank sprocket.

Good luck with it!
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