Anytime ive changed an engine i put it in with the box attached, just make sure to angle the box down so it goes in first then lower the engine down and bolt in the mount, then just jack the box back up and bolt it up! I think that way is easier than having to bolt the box to the engine in the bay.
Paid 20 euro for mine, bracket was broke so had to screw it to the handbreak surround but armrest itself is perfect! I think anyone who pays £160 is tapped in the head
A front under strut would help tighten the front end a bit and if you don't already have a rear boot strut get one along with a whiteline rear arb and that will tighten the arse end right up :D