The generator matrix

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

generates a code of length 24 over GR(64,4) who´s minimum homogenous weight is 136.

Homogenous weight enumerator: w(x)=1x^0+679x^136+2142x^144+448x^147+3227x^152+9408x^155+5320x^160+65856x^163+7357x^168+153664x^171+8386x^176+4417x^184+1239x^192

The gray image is a code over GF(8) with n=192, k=6 and d=136.
This code was found by Heurico 1.16 in 11.7 seconds.