There are several ways to convert a MG-13 mag to fit a Hakim. The easiest way is publicized here http://www.geocities.com/Yosemite/Gorge/4653/hakim3.htm
One word of caution about “the easy way” is that you will have to permanently modify your Hakim magazine well to accept the mag. I do not recommend doing this procedure on ANY complete (or nearly complete) Hakim. I understand that many people have bought worn-out warhorses from RelicHunter that are missing many hard-to find parts. People who bought one of there just want to make their Hakim function and are using parts from other makes/models or making many parts them self. Anyway, I have no problem with people in this scenario altering their mag wells, but I would hate to see someone alter a complete and original rifle.
The hardest way is altering the mag in such a way that it fits in an un-altered rifle. This will entail the use of a torch and silver solder/brazing rod OR careful use of a MIG welder. It would take me quite a wile to go through the step by step procedure on how to do this (along with pictures, to help you understand) BUT is will try and save you a little trouble and recommend that you just buy one from jb5734 (Gunboards member) He has the tooling set up to mass produce these and they are TOP NOTCH QUALITY. In my opinion, he sells them for a very fair price (I think around $70.00).
I have 18 years of metalworking experience and, although not too difficult, it is a very time consuming process. Back when I did mine, MG-13 mags could be had for less than $7.00---now they cost $25.00++. A novice will have a very good chance of destroying a mag trying to weld on thin 80 year-old, rusty metal.
Honestly unless you have an old parts rifle---buy one of jb’s mags. You wont be disappointed.