Just pipe your unfiltered output into a single instance of grep and use an extended regexp to declare what you want to ignore:
grep -Ri 64 src/install/ | grep -v -E '(\.svn|file|2\.5|2\.6)'
Edit: To search multiple files maybe try
find ./src/install -type f -print |\
grep -v -E '(\.svn|file|2\.5|2\.6)' | xargs grep -i 64
Edit: Ooh. I forgot to add the simple trick to stop a cringeable use of multiple grep instances, namely
ps -ef | grep something | grep -v grep
Replacing that with
ps -ef | grep "[s]omething"
removes the need of the second grep.
HTH
cheers,