Hi there, welcome to the site. Congratulations on the seal 28! Great boat! Although i am bias :)
I've had no official training as such, but on my last boat, i propped up each corner to take the weight off whilst i changed each mount individually. There are some very elaborate methods to make sure your gearbox lines up with and angled correctly to the propeller shaft. This is very important so make sure it's done correctly. Any error and you risk vibration at the very least, which can also cause other failures to occur.
Good luck,
Lee