The only race that could match your description is Zandvoort 1971
If you go to this site
and click on “races” then “Formula One” on the left colum, then on the year 1971 and then Zandvoort further down it will tell you (in swedish)that he started the race in 13th position on a March, that the weather was bad with episodes of rain and that he moved ahead of the field, ending the race in fourth position after passing Surtees in the last laps. Could it be it ? And by the way that is the most accurate and complete website about SuperSwede. Most of it is in English but some is only “paa svenska”. It will give you a good resumé of every race Ronnie participated in.