As already asked, is your Park Ave the Naturally Aspirated version, or the Supercharged version?
I have not replaced one on a 97', but on my 96' PA Naturally Aspirated it was pretty easy, I did not have to remove any engine mounts, I did have to remove the power steering pump and hang it with a bungee to my hood, I was not careful when I removed the last bolt to the power steering pump though, and I let it drop onto my oil pressure sensor, which bloke it off.
If you have the Supercharged motor I do believe you have to remove that bracket, but I don't think jacking it up will help, that may make it harder, all you should have to do is use a jack with a nice wide/thick piece of wood, like a 2x6 that Stephen suggested, that way you do not damage your oil-pan, after those 5 bolts are removed you should be able to lower the jack a little, and that should let you remove the support bracket.
Hopefully somebody that has actually removed that bracket can provide some more insight for you.
2006 Pontiac Grand Prix GT with SC
1996 Buick Park Ave NA