How i did it:
At first i flushed the pen, got the friction fitted feed out, and replaced the nib with the flex one i had, aligning the first slots on the feed with the ones on the nib. Then i heat setted the feed on the nib, by clamping the tip of the feed with the nib and putting it in boiling water until it set. Then i took everything out, and eith a razor and a lot of patience made the ink flow slots larger and deeper, so that it would improve ink flow, i put everything together, rinsed it thoroughly and then proceeded to add ink. I added Montblank Mystery black, and when it was in the converter, i took it out, dipped the tip of a needle in dish hoap and added an extremely small amount by dipping the needle in the converter. I proceeded by priming the nib, letting two drops fall and then started writing.
IT'S SO MUCH FUN!!!