Not trying to dispute your engine as genuine but only trying to help understand what the situation could be...
Even if the line worker mistakenly slipped a '2' instead of the correct '1' in at the start of the sequential six of the #'s in the gang holder, it appears even the last five #'s would still indicate over 800 units beyond production?.
How's the broaching look?.
Also interesting is Colvin's 'no plant note' as just last week I was looking at the #'s of an NCRS Top-Flite Survivor '65 Fuelie and am pretty sure it had the F..
It was also a March engine build but earlier in the month and on casting # 3782870 ..
~ Pete
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I like real cars best...especially the REAL real ones!