You should use 20w 50 motor oil in it. "SL" is just the API oil classification from about 2001 - 2004 or so. Today's oil is "SN" rated.
If the Rotella is 20w50 then use it. If it ain't, then don't use it.
But, hey, it's your unit, put what ya want in it.
It ain't rocket science!
'Course if yer house has more wheels than yer truck...
" Old age ain't for sissies "