Richard,
By September 1944 most 8th AF Fighter Groups with P-38s had converted to P-51s, with the possible exception of 479th FG.
The Roermond case more likely involves one of the three 9th AF Fighter Groups that had the P-38: 367th, 370th or 474th.
Unfortunately an USAAF chronology like this one on
http://www.usaaf.net/chron/44/sep44.htm does not really point to attacks in Dutch Limburg on 1 September 1944, so a Group history should provide a conclusive answer.
Regards,
Leendert