.........provide yourself with a 1mm cutting disc and a marker,that's all you need-and maybe some skills,but it isn't as dramatically as it looks !
1: here we start you can see the cuttings i've marked before ? Its' very important to cut as straight as possible,because it makes all further work easier,it's like a railroad: how and where you start definates where you end.
2: the other Side :
3: That's what you get then , you've to close the hole by using a special section out of the removed left header
4: here it is,this is the removed left header,and the
Section you need i've marked white.
Its very Important to cut out the Section with a + of 1 cm everywhere,in Germany they say: twice time cutted and still too short.
5:I've marked it pink on this picture,where exactly the cutting line is,now we're at the Spot where you need some skills.
6: so,compare this Pic with the one above,to cut out the lid you need you've to be careful,if you do this the first Time keep more Material the first cut,than you need ,try to put on the cover,take a close look which edge maybe to remove now,then: take a 2nd look,and then cut again.
7:As mentioned above,this is the raw result you get,you see a few mm's missing horizontally ,but as mentioned at 1. ,if you've cutted very straight at the beginning it's not a big deal yet,you only have to cut straight to make it fit.
8: the view from top,always consider it's a 3-D cutting Job, so if you pull a line with your marker to cut there,always have a look if the whole thing fits on the other sides still too.
9: very detailled here: you probably wont be a able to get a 0.5 mm gap everywhere,sometimes that happens by fortune,but you can live with gaps of 1-2 mm,that's no Problem for a good welder.
10:Very large if you enlarge,that's the final result,you see i've got up to 1mm gap too.It would have been possible to reach nearly 0,but it's superflouos,it's as good weldable too.
A Comparison here: Acra modified in 1 ,a Moriwaki in 2 and Acra std. in 2 Section