Not sure what you are asking here but if you want to know what the engine is, Roush stamps the engine build number on the back of the engine. Then you will need to phone Roush and ask them what the build specs of that particular engine number are.
In general, if it has a dual plane intake manifold with a 770 Holley Street Avenger carb, it is an SR. If it has a single plane manifold with a Holley double pumper, it is an R.
If you want a great street engine, get the SR. If you want more of a race engine, get the R.
But, most importantly, check the
oil consumption on the engine you are considering. Several of us have had expensive repairs due to this problem. Roush engines are noted for having looser ring tolerances (as specified in their engine warranty) and can consume significant amounts of
oil. If possible, run a leakdown test on the engine in question before you pay for the car. I'm sure most Roush engines are running just fine, but make sure that includes the one you are thinking of buying.
For more info, check out this thread.
Roush Engine Warranty Exclusions.