drill out spot welds on gearbox mount on passenger side chasis leg. attach the whole mount to the gearbox, including the metal bracket that you have just drilled the spot welds out of onto the gearbox.
mount engine on other 2 mounts and use jack to position correctly. mark where passenger side chasis leg gearbox mount lines up, drop engine out, remove moutn from box, weld it onto chasis leg, re fit engine to check, then fully weld mount on.
need lowered tie bar brackets aswell as they catch the gearbox, depending on lwering, thats how i did it, easy. i had a bare block in the garage though, so just bolted g/box onto that, made it easier than fitting the whole engine.
cheers