Making engine mounts, your tips please!

[jps]

I sense a weekly ritual of asking advice... I am really struggling with making my engine mounts. I tacked some together a while ago with the engine dangling from the crane. I found that, when I took the weight of the crane the land rover rubber mounts compressed and the engine dropped from where I'd positioned it...

I've ground the welds off and am starting again.

Today I tried supporting it from underneath with wood, but it just rocked about as soon as I touched it.

Plus, actually cutting the box section to fit is a HELL of a challenge, any tips on that?