while I understand the idea of poly bushings over rubber for a tighter suspension on a corner carving rail, I'm not sure if they're really worth the money over rubber for normal use. But then I've never priced them myself so I can't say what the price difference is. Seems that as long as the rubber ones last from the factory that good rubber replacements would be fine. Spring bushings on hard used suspensions may be a different story though. Now for a t-case mount, I'd think factory style replacements should be just fine.
For jack placement I'd think any sturdy place on the case or tranny would be fine, just not the pan. And make sure it's all sturdy and mabey even strapped to the jack pad to keep it from getting knocked off. And I'd raise it just enough to replace the bushings to keep from tearing or pinching something that may cause problems later. may be best not to lie directly under it just in case too.