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

generates a code of length 64 over GR(64,4) who´s minimum homogenous weight is 400.

Homogenous weight enumerator: w(x)=1x^0+189x^400+1267x^408+2135x^416+2926x^424+3297x^432+3969x^440+28672x^441+4333x^448+200704x^449+4396x^456+4137x^464+3094x^472+1974x^480+784x^488+231x^496+28x^504+7x^512

The gray image is a code over GF(8) with n=512, k=6 and d=400.
This code was found by Heurico 1.16 in 41.1 seconds.