It's easier, if a little messier to remove the engine and trans as one unit. Just some extra steps, undoing the shift linkage at the trans, removing the transmission cooler lines (line crow foot wrenches help a lot on the transmission side), removing the trans mount nut, and driveshaft. Remove the yoke straps at the axle (car should be up in the air on 4 jack stands), may need a pry bar to get them loose, and don't let it hit the ground and damage the yokes on either end. You can make a cover for the trans so it doesn't puke everywhere with a 20 or 16oz pop bottle and some duck tape or zipties. Cut the top of the bottle off and slide it over the transmission, securing with tape or zipties. Fits like a glove.
For engine mounts, go to your local parts store and ask for some from a g body with a 5.0 305 V8... like an 87 monte carlo SS. Has to be a 305, not a 307. Both are 5.0L engines, but the 307 is an oldsmobile engine and uses different mounts. Has to be a 305, monte carlo SS is the easiest car to choose from. Yes, 305 mounts fit on a 350. If you walk in there telling them you're swapping engines, they'll look at you like you're speaking Japanese. "If it's not in the system we don't have it.". pfft.
Anyway, as said above plenty of knowledge in here, willing to bet 99% of people on this site have done what you're about to at least once.