I found several papers on grafting jackfruit onto marang, but none for marang onto jack. There is a good probability of eventual failure, but it's a neat experiment for me in the meantime.
I approach grafted the marang onto the jack back on January 2. As you can see, the graft is very secure and the bark is starting to close in on the graft site. I'm being very patient/cautious. I plan to leave the root ball attached until more of the graft is covered, then I will slowly cut away below the graft.
Today I removed the huge branch the graft is on. Hopefully this will direct more energy into the graft. I will remove the rest of the branches after this as well. I want to keep them for now to support the whole tree. The jackfruit itself is pretty much a dud and I would have removed it, but we'll see how this pans out.