This does list the 757th and other major allied units involved in the Italian Campaign.  This DOES include your grandfather's unit.  Yeah!   
 
http://www.milhist.net/ordbat/mtounits.html
 
Here's a contact name for all companies of the 757th Tank Bn:
 
Mr. Warren & Nancy Davis at 1-612-484-8229
 
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More info:
 
This site talks about the 752nd and 757th Tanks Bns:
 
http://www.752ndtank.com/RocketTanks.html
 
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Please see the Red Bull's site (34th Infantry Div).  Your grandfather's unit was attached to them.  
 
http://www.34infdiv.org/
 
Who Were We?
 
WW II Order of Battle - 34th Infantry Division
Headquarters, 34th Infantry Division 
133rd Infantry Regiment 
   100th Infantry Battalion (Separate) [assigned Naples-Foggia, Anzio, Rome-Arno] 
135th Infantry Regiment 
168th Infantry Regiment 
   168th Commandos 
442nd Regimental Combat Team [attached Rome-Arno] 
   442nd Infantry Regiment 
      100th Infantry Battalion 
   232nd Engineeer (Combat) Company 
   442nd Medical Detachment 
   522nd Field Artillery Battalion (105mm) 
34th Division Artillery 
   34th Division Artillery Headquarters and Headquarters Battery 
   125th Field Artillery Battalion (105mm) 
   151st Field Artillery Battalion (105mm) 
   175th Field Artillery Battalion (105mm) 
   185th Field Artillery Battalion (155mm) 
34th Cavalry Reconnaissance Troop (Mechanized) 
109th Engineer (Combat) Battalion 
109th Medical Battalion 
34th Division Special Troops 
   Headquarters, Special Troops, 34th Division 
   34th Infantry Division Headquarters Company 
   34th Infantry Division Band 
   Military Police Platoon, 34th Division 
   34th Counter-Intelligence Detachment [attached] 
   34th Quartermaster Company 
   34th Signal Company 
   734th Ordnance (Light Maintenance) Company 
 
Other Attached Units
 
Jewish Infantry Brigade (attached Occupation) 
A Company, 2nd Chemical Warfare Battalion (attached Naples-Foggia) 
35th Quartermaster War Dog Platoon (attached North Apennines) 
38th Infantry Scout Dog Platoon (attached Occupation) 
72nd Signal Company (Special) (attached Naples-Foggia) 
84th Chemical Mortar Battalion (attached North Apennines) 
100th Chemical Mortar Battalion (attached North Apennines, Po Valley) 
105th AAA Automatic Weapons Battalion (Self-Propelled) (attached Naples-Foggia) 
107th Coast Artillery Battalion (AAA Automatic Weapons) Battalion (attached Tunisia) 
A Company, 191st Tank Battalion (attached Naples-Foggia) 
2nd Battalion, 351st Infantry Regiment (attached North Apennines) 
432nd AAA Automatic Weapons Battalion (attached North Apennines) 
435th AAA Automatic Weapons Battalion (Self-Propelled) (attached Anzio) 
443rd AAA Automatic Weapons Battalion (Self-Propelled) (attached Tunisia) 
751st Tank Battalion (attached Tunisia) 
752nd Tank Battalion (attached Rome-Arno, North Apennines, Po Valley, Occupation) 
753rd Tank Battalion (attached Rome-Arno) 
757th Tank Battalion (attached North Apennines) 
776th Tank Destroyer Battalion (attached Naples-Foggia) 
804th Tank Destroyer Battalion (attached North Apennines) 
807th Tank Destroyer Battalion (attached North Apennines) 
813th Tank Destroyer Battalion (attached Tunisia) 
and still other units which remain to be found, confirmed, and listed here.