You have two options, dismantle enough to be able to raise the engine/box, or just hacksaw the head off, then replace upside down, making sure to use a NEW nyloc locknut and thread lock, if the car is a auto you will also need to shave a tiny amount of the bolt head, even better than locknut though is a K nut, easy to make, just squeeze the nut in a vice until slightly mishapen whereupon it will grip on the threads real tight.
I always install upside down, never seen any one have any issue with this way.
tabetha