RE: Lowering of engine on thrust line
I would agree with Tall Paul. The only thing you might have to change is the thrust angle if you moved it down[or up]. Just look at some of the designs of that have been made. Like the P6E for one. See how low the engine sits in that one. then look at flying boats with their engines on top. Just have to have a thrust angle that will make them fly right. Hope this helps.