I wouldn't buy a timing light just yet. Most likely dealing with high resistance in the starting circuit, whether it be cables, connections or the starter itself. Sounds like you are on the right track.
The crane unit is indeed an externally mounted electronic ignition. I believe they use the stock rotor.
Two 14" 5 lug S5 wheels with ST205/75R14 Kenda Loadstar radials $349
Two 14" 5 lug S5 wheels with ST215/75R14 Kenda Loadstar radials $389
Two 15" 5 lug S5 wheels with ST205/75R15 Kenda Loadstar radials $409
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