slc5 to a siemens platform

What is the success rate for importing a project / Migrating it across from Rockwell Slc5 to Siemens?

Can it be done?

Will it need a lot of rework?

What tools do I need?

What is the best target S7-300? S7-1200 ?S7-1500?

Siemens will do this conversion for you (I seem to remember they also gave me the software to do it from a PLC5). However the end result was atrocious and I ended up regretting not starting it from scratch and copying over some of the rungs and conditions rather than a straight copy.

The reason is that although the system will work as it did on the SLC, troubleshooting is really hard. TIA Portal is made to display the variable name prominently and not so much the comment on the variable. As such your code then becomes a mix of N, B and F files which don't necessarily have much relevance to the person troubleshooting.
The SLCs also don't make use of re-usable code which is something you can leverage in a Siemens PLC to write and test less code.

I'd look at a S7-1500... depending on the processor and program size, it's possible the 1200 will run the program, but it does limit the options and upgrades possible in the system greatly and may not even be enough for all the IO you need.

Manual re-write.

+1 that instead of arranging the data in the arcaic style of one data type -> one data file, the data should be arranged in whatever grouping is most sensible for the objects or functions that there are in the program.

Other than that, pure AB Ladder code translates pretty much 1-to-1 into S7-1500 ladder code.

If it is a very small SLC5/01 or SLC5/02 or brick with fixed I/O, then an S7-1200 could do the job.
SLC5/03 or bigger, I would go for an S7-1500 CPU. Even a small S7-1500 can easily fit the program of an SLC5/05 64k.