Did the mods some years ago and the guide i made on my computer is at my ex wife's house. You can go by. Took me 4 years to get my cars back...
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Years ago i found a polish website dedicated to this subject but you could not copy paste the page to put it in a translation device of website. So i spent weeks to manualy input the polish sentesses into a translationwebsite to get a manual or a guideline.
It's a while back , but i used a bis crank and conrods. Beetle cilinders and piston. I welded up the top inside of the cranckcase and in between the holes were the cilinders go. Made the holes a little bigger and fitted the beetle ones. Now i have to make up a plate , but i do not know how thick. Thats the stage where i am now. I found my mojo back a while ago , so i have to look for the polish website again. There are pictures on that site for reference.