I think the nuts are on the inside of the hood. So if it were me, I would set up a table right under the hood where it's flipped. You may have to use 2x4s or something to make it high enough but you should be able to lay the new grill right in there without taking the hood off.
Best way I’ve found, 4 - 7/16 nuts in each inside corner. Rubber mounts/ bolts might break. If so you’ll need to replace mounts,on grill before re installing.