Hi Tobias
I've done some rough things with Austin sevens but never seen an axle break like that!
Perhaps you should put up the photos in the forum chat for opinions as to why it has broken like that.
I personally don't like the way the front spring appears to almost be touching the axle beam so when hitting a bump must be bottoming out? Also the main leaf has been reversed to lower the car further.
I purchased a bowed front axle axle from Tony Betts on uk 01162 867522 recently,he may be able to help.
Regards
Dave