As woodsman said that has been hacked.
Some frames did come with a removable section to make the removal of the engine easier.
You could get that welded back together with slugs in the joint to reinforce when putting it back together.
Either that or cut the correct overlapping joints off of another frame that have them as standard and have them welded in.
Either way as it stands its dangerous and i would be pissed off to find that on a bike i had just bought.
Some frames did come with a removable section to make the removal of the engine easier.
You could get that welded back together with slugs in the joint to reinforce when putting it back together.
Either that or cut the correct overlapping joints off of another frame that have them as standard and have them welded in.
Either way as it stands its dangerous and i would be pissed off to find that on a bike i had just bought.