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**'68OrangeSunshine** · 08-22-2005, 04:44 AM

If the shifter is on the column, you have a Saginaw transmission. If the shifter is on the floor --it's considered a 4-speed (even if a "granny -1 -2 -3" set-up). If that's the original tranny, it would be an SM420. If someone put in a later 4-speed, it could be an SM465. '67 was the last year for the 420 in US production.
Good news is the transmission bolt pattern is the same, be it L6, SBC V8 or BBC V8. Unlike the competition, GM was into versatility and interchangability.
Only ripple is the Saginaw bellhousing has too small an opening for the front flange of a 465. [Don't know about the 420's fit.] Otherwise the bellhousings are identical.
Anyway an SM420 or 465 behind a 454 should be no problem. You might have to upgrade the flywheel to 11" or 12" -- depending on what diameter is in there now. 250s came with 10" or (?)10.5" and 292s usually came with 11" flywheels. [Until '72 when it bumped up to 12"].
I'm not familiar with the Saginaw unit to say how well it would do behind a big block. It could be cool, or it could be a grenade.

08-22-2005, 04:44 AM	#2
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,641	If the shifter is on the column, you have a Saginaw transmission. If the shifter is on the floor --it's considered a 4-speed (even if a "granny -1 -2 -3" set-up). If that's the original tranny, it would be an SM420. If someone put in a later 4-speed, it could be an SM465. '67 was the last year for the 420 in US production. Good news is the transmission bolt pattern is the same, be it L6, SBC V8 or BBC V8. Unlike the competition, GM was into versatility and interchangability. Only ripple is the Saginaw bellhousing has too small an opening for the front flange of a 465. [Don't know about the 420's fit.] Otherwise the bellhousings are identical. Anyway an SM420 or 465 behind a 454 should be no problem. You might have to upgrade the flywheel to 11" or 12" -- depending on what diameter is in there now. 250s came with 10" or (?)10.5" and 292s usually came with 11" flywheels. [Until '72 when it bumped up to 12"]. I'm not familiar with the Saginaw unit to say how well it would do behind a big block. It could be cool, or it could be a grenade. __________________ Every 25 years I like to rebuild that 292, whether it needs it or not. Last edited by '68OrangeSunshine; 08-23-2005 at 07:07 AM.