Can someone tell me if a piston from my 1963 Avanti's R1 engine is
 the same as the "grocery getter" engines of the same year?

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   No, it's a special skirted flat top piston, they are only about $5
more each than the regular 289 piston anyway.

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Doug:
No... the pistons are different, but interchangable.
The standard 289 engine pistons are the same size as the Avanti R1 pistons,
but the standard pistons have "dished" tops to lower the compression ratio.
(in '63, that would be about 8.5:1)
Avanti pistons are flat tops, which raise the compression ratio.
But that's not to say that you can't interchange the pistons.  I know
people that have rebuilt standard 289 engines using R1 pistons, and R1 289
engines, using dished 289 standard pistons.

But don't try to use pistons from a 259 engine in a 289, of any variety.
The 259 pistons are also flat top pistons, but the wrist pin that the
connnecting rod attached to is located in a different place; 259 pistons
will only work in an engine with a 259 crankshaft, and 289 pistons will
work in any engine with a 289 crankshaft....
Rods are the same in both engines.
Lew
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No
R1 and R2 pistons are flat top Alum. 289 pistons. Regular 289 pistons had a
dished top there fore lower compression. 259 pistons were also flat top but
the wrist pin was lower than 289 pistons. 
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