The lower shrouds will hold the mast up. I would also shackle some part of the middle turnbuckle to one of the other ones.

The jackstands hold little weight. Its a stiff boat. I don't think you'll have a problem when you remove the bulkhead. The only alternative would be to fashion some temporary braces for the interior, which would make the work more inconvenient.

My Sawzall and I would be happy to pop over to Brooklyn and poke around

Tony G performed a Double Bulkheadectomy on his Ariel. Check out "Fruits of My Labor" in the Gallery section.

Cheers