That's part of what would need to be done, but I don't think it's quite everything. For instance, all of these new bigtop-packages/src/*/spark1 scripts, specs, etc., would need to be changed such that they are using Spark 1-.x-specific paths, package names, version variables, etc. (e.g., instead of referencing $SPARK_VERSION, it should use $SPARK1_VERSION, and instead of installing things to /usr/lib/spark, they should install to something like /usr/lib/spark1.) Also, what about duplicating the Puppet modules for Spark 1? Wouldn't you want that too? If so, you need even more changes to distinguish Spark 1.x from Spark 2.x.
All of this complexity is why I was hoping not to have Spark 1.x and Spark 2.x colocated in the same version of Bigtop, but at least I'm happy with having the "main" (i.e., un-suffixed) version of Spark be Spark 2.x (instead of having "spark2").