261st Infantry was an element of 65th Infantry Division. 811th Tank Destroyer Battalion was non-divisional - as were all such units - and was attached to several major commands during the war. 74th Field Artillery Battalion was also non-divisional and didn't reach Europe until late in the war (January 1945). The other unit you refer to is probably the 90th Replacement Battalion. It all seems like a bowl of spaghetti and the only way I know to untangle it is by accessing official records and that, of course, costs.