The low temperature (T<70 K) specific heat obtained for the UCu_4+xAl_8-x derivatives in which the 3d elements (Cr, Mn and Ni) have been substituted for Cu, and Ga for Al is presented. The parent alloys have exhibited an alloying induced transition from simple antiferromagnetic ordering for low Cu--concentration (for x \leq 1.25) to heavy-fermion-like properties (for x \geq 1.5). The crystallographic disorder introduced by a change of stoichiometry could be the reason for enhanced \gamma . These components slightly change both the crystallographic relations and electronic structure, and the determined thermodynamic data strongly suggest other reasons for an enhanced \gamma than crystallographic disorder. The occurrence of the T³ \ln T term in specific heat for all alloys except that of Ni provides the conclusion about spin fluctuation state. The Ni compound is antiferromagnetic below T_N=27.5 K.

PACS numbers: 71.20.Lp, 71.27.+a, 75.40.Cx