I put the book where i could find it easily ; in the draw .
got
GS 45 It. 40 china G 51 It.( C.L. )
Ex 73 ( 146 ) 74 ( 148 ) 68 ( 136 .
Tr. 60 ( 120 ) 56 ( 112 ) 58 ( 116 )
Bt. 58 ( 116 ) 56 ( 112 ) 58 ( 112 )
io 44 ic 47 44 - 46 47 - 47
so crank timings pretty much the same , sleeve set ups not .
Dunno how the Blow Down relates to the stunt pipe use ,
The 40 has the most , the G 51 R/C would have more than the C/L ! maybe better than C/L , when both piped ? .
The OS 40 / 46 VFs run about 140 Ex 120 Trans , as incidently My Silver Head ( Early ) X 45 Chrome/ ringed sucker .
The X 45 has long nose 21/46 bolt pattern NOT G Series mount .
Other X 45s have a bit , and much on flat head , higher sleeve timing .
The Como & G have same mount tho Comos shorter nose , theres two series Como post baffled ring ,
some 40 baffle are ABC , stamped on lug. Schnurle are truncated block / Flat Head .
You had me thinking of ' G ' crank swaps for timing / displacement changes . Shorter Stroke lowering port timing & V.c.V.