The generator matrix

 1  0  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  0  1  1  1  1  1  1  0  1  1  1  1  1  1  1  1  2 2a  1  1  1  1  1
 0  1  1  a 3a^2+2 2a^2+3a+1 a^2+3a a^2+3a+3 3a^2+2a+3  a 3a^2+2  0 2a^2+3 a^2+3a+3 a^2+3a 3a^2+2a+3 2a^2+3a+1  1 2a^2+3 a^2+3a+3 2a^2+3 3a^2+2a+3 2a^2+2a+1 3a^2+2  1 a^2+3a+1 2a+1 3a^2+3a+3 3a^2+a+1 2a^2+3a+1  0 2a^2+2a+1 a^2+3a+1  1  1 a^2+a a^2+3a+1  a a^2+3a a+2
 0  0 2a^2+2  0  2  2 2a+2  2 2a^2 2a+2 2a^2+2 2a^2 2a^2  0  0 2a^2 2a^2+2  2  2 2a 2a^2+2 2a+2 2a^2+2a 2a^2+2 2a^2 2a+2  2  2 2a^2+2a 2a+2 2a^2+2a 2a^2+2a 2a+2 2a^2 2a^2+2 2a^2  0 2a^2+2a 2a^2+2a 2a+2
 0  0  0  2 2a^2+2 2a^2+2a+2 2a+2 2a^2 2a^2+2a+2 2a^2+2 2a^2+2 2a^2+2a 2a 2a^2 2a^2+2a+2  0 2a^2+2a 2a^2+2a+2 2a 2a+2 2a^2  0  2 2a+2 2a+2 2a^2+2a 2a^2 2a^2+2a 2a^2+2a+2 2a^2+2 2a+2 2a^2 2a^2+2a+2 2a^2 2a^2+2a 2a^2+2 2a 2a^2 2a^2+2 2a^2

generates a code of length 40 over GR(64,4) who´s minimum homogenous weight is 256.

Homogenous weight enumerator: w(x)=1x^0+539x^256+224x^259+392x^260+504x^261+1848x^263+3045x^264+4704x^267+4200x^268+2968x^269+3864x^271+5411x^272+32928x^275+19096x^276+10472x^277+11816x^279+12509x^280+76832x^283+33656x^284+14728x^285+11144x^287+10276x^288+371x^296+343x^304+259x^312+14x^320

The gray image is a code over GF(8) with n=320, k=6 and d=256.
This code was found by Heurico 1.16 in 8.56 seconds.