To add to what sixpack said-
As far as different stroke, the strokes are the same. If the 261 rod is different length, he could have referred to rod/stroke ratio or perhaps even bore/stroke ratio.
Most oversize pistons do come with a slightly lower deck height built in. This serves two purposes: One- it keeps the compression ratio the same as stock and to prevent the piston from sticking out above deck on a block that's been shaved on an earlier build. I was told this by a pontiac engine builder. TRW forged flattops can end up .020 to .050" down in the hole depending on oversize used and tolerance stack-up. This will cause detonation problems on high compression ratio V8s due to the small unswept volume above piston.
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