The generator matrix

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

generates a code of length 91 over GR(16,4) who´s minimum homogenous weight is 256.

Homogenous weight enumerator: w(x)=1x^0+258x^256+864x^257+792x^258+732x^259+1077x^260+2112x^261+1596x^262+1680x^263+1584x^264+3384x^265+2136x^266+1632x^267+2040x^268+4128x^269+2532x^270+2232x^271+2169x^272+4212x^273+2676x^274+2004x^275+2418x^276+3648x^277+2448x^278+1872x^279+1854x^280+3012x^281+1656x^282+1236x^283+1116x^284+2148x^285+1008x^286+660x^287+609x^288+768x^289+456x^290+204x^291+165x^292+300x^293+48x^294+36x^295+18x^296+12x^298+3x^304

The gray image is a code over GF(4) with n=364, k=8 and d=256.
This code was found by Heurico 1.16 in 30 seconds.