POST#16-
I Reckoned ebay would be a great place to research GL1000 flywheel rim timing marks . My researching efforts end here
Looks like 1978 and 1979 crankshafts, consistently, utilized the T 1 F and T 2 F timing marks scheme stamped on their flywheel rim. The 431 ignition advancer assembly matches up with this one.
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Screenshot 2022-10-03 130346 1979 GL1000 CRANKSHAFT-eBay.jpg
Looked at 6 crankshafts individually listed as 1975, 1976, 1977 production years engine pieces. All 6 flywheel rims utilized the identical T F 1 and T F 2 timing marks stamping scheme. The 371 ignition advancer assembly matches up with this one.
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Screenshot 2022-10-03 125516 GL1000 CRANKSHAFT.jpg
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EUREKA

The 1975-1977 engine group has slightly different ignition advance static timing degrees specs. and camshaft profile, when compared to the 1978 and 1979 engine group ignition advance static timing degrees specs. and camshaft profile.
There is the answer. The additional 5 degrees of BTDC static timing advance stamped onto the 1978-1979 crankshaft flywheel rim then provided the opportunity to reposition the 'indicator' number
between their respective T and F letters.
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Screenshot 2022-10-03 225404 F MARK static ignition timing degrees specs.jpg
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DONE !! 
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Cliff

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Cliff
'75 GL1000 home built trike;
http://www.ngwclub.com/forum/viewtopic.php?f=30&t=39996
October,2017 BOTM
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previous rides:
1953 H-D Servi-car, naked, 1969-1978 (serial#53G1559 committed to memory!)
1980 CB900 Custom (triked) 1997-2003 .... R.I.P.