Bluebird - assuming you misread an "S" for a "5", and that you meant 964-S; then you have a aftermarket replacement for a 1937 - 1962 Chevy 216.
I would not suggest this unit for a 270. Find a Chevy dude with a 216 and sell him the unit; then locate either the original Zenith, or another carb capable of feeding your 270.
To determine your original carburetor, try this link:
http://www.thecarburetorshop.com/TRGMC.htm Jon.
