The generator matrix

 1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  2  1  1  1  1  1  1  2  1  1  1
 0  2  0  0  0  2  2  2 2a  0  2 2a 2a 2a 2a  2 2a 2a^2+2a+2  0  0  2 2a^2+2 2a^2+2a+2 2a+2 2a^2 2a+2  0 2a+2 2a^2 2a^2 2a^2+2a+2 2a^2+2a+2  2 2a^2+2a 2a^2  2 2a^2+2a+2  2  0  2  2 2a^2+2a  0
 0  0  2  0  0 2a^2+2 2a^2+2a+2 2a^2+2a 2a^2+2a  2 2a+2 2a^2+2  0  2 2a^2+2a+2 2a^2 2a 2a^2+2 2a^2 2a  0 2a^2+2a  2  0 2a^2+2a 2a^2 2a^2 2a^2+2 2a^2  0 2a^2+2 2a^2+2a+2 2a^2+2 2a^2 2a^2  0 2a  2 2a^2+2 2a^2+2a+2 2a+2 2a^2+2a  0
 0  0  0  2  0  2 2a^2+2a+2 2a 2a+2 2a^2 2a^2+2  0 2a^2+2a+2  2 2a 2a^2+2a 2a^2+2a 2a^2+2a  2 2a^2+2a 2a 2a 2a^2+2a 2a^2+2a 2a+2  0 2a^2  0 2a^2+2a  2  0  2 2a  2  0 2a 2a^2+2a 2a 2a^2 2a^2+2a+2 2a^2+2a+2 2a^2  0
 0  0  0  0  2 2a^2+2 2a+2 2a 2a^2+2a+2 2a 2a^2 2a^2 2a+2  0 2a  0 2a^2 2a^2+2a 2a^2+2a  2 2a+2 2a^2+2a+2 2a^2+2 2a+2  2 2a 2a^2+2 2a^2  2 2a^2 2a^2+2a+2 2a  2  0  0 2a^2+2  0 2a 2a^2+2a 2a^2 2a 2a^2+2a  0

generates a code of length 43 over GR(64,4) who´s minimum homogenous weight is 256.

Homogenous weight enumerator: w(x)=1x^0+154x^256+1043x^264+2030x^272+3164x^280+3584x^287+3493x^288+50176x^295+4767x^296+175616x^303+5530x^304+5390x^312+4466x^320+2044x^328+630x^336+56x^344

The gray image is a code over GF(8) with n=344, k=6 and d=256.
This code was found by Heurico 1.16 in 25.3 seconds.