The generator matrix

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

generates a code of length 39 over GR(64,4) who´s minimum homogenous weight is 256.

Homogenous weight enumerator: w(x)=1x^0+2352x^256+392x^259+1288x^260+4256x^261+10920x^262+6496x^263+12656x^264+448x^266+5488x^267+8176x^268+14784x^269+22960x^270+8512x^271+18396x^272+3136x^274+19208x^275+19208x^276+27552x^277+37800x^278+13664x^279+24339x^280+56x^288+49x^296+7x^304

The gray image is a code over GF(8) with n=312, k=6 and d=256.
This code was found by Heurico 1.16 in 7.37 seconds.