You could use JB Weld, since people use it to seal turbo oil return fittings, and it holds up fine. Although, there isn't much pressure in the return fittngs, except that due to gravit, and your oil pressure sender location typically sees anywhere from 30-90psi, so that might be a problem in the future. I would say if you absolutely have to have it running, then JB Weld should be an adequate temporary solution. I would have it taken care of properly in the future, since I don't know how well JB Weld stands up to pressure. In any case, I would make sure the JB Weld has ample time to cure before trying to crank the engine over. You have an extra B16? Is there a reason why you can't just swap that block in? I would do that, if it's a viable option.