The B18FT from a 400 series turbo (440, 460, or 480) will pretty much bolt right in. You'll have to play with both manifolds a fair bit, and probably use a hybrid of mounts, etc.
You'll also need to strengthen the prop. The standard ally / rubber prop on the Mrs' 340 slips a bit if you try to dump all the mighty 72 horses from its 1.4 lump, never mind a turbo unit.
Take a look here for more info on the conversion...
www.huskyracer.50megs.com
cheers
James