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Unfortunately, my copy of Rendezvous with Destiny has gone missing, but what I remember was that the 101 was resting and refitting at Mourmelon when the order came to go to Bastogne, and any means of transport available was pressed into service, without distinction of who the equipment originally belonged to. Then once in and around Bastogne, there were so many units attached, in such an ad hoc manner, and so much abandonned equipment recovered and pressed into use, you could probably get away with using almost any vehicle in your diorama and reasonably defend its use.
I know for certain that of non-organic units there were a tank destroyer battalion (the 705, I believe, which used M-10s), at least 2 engineering bn's, an armored artillery bn (maybe the 755), the 771 and 969 field artillery bns (African-American troops) and others. Then there were remnants of other units ... Good luck with the dio.
Al.