Most of the USA conversions I have seen done involved moving the engine mounts over to the frame rails and are secured at the top of the frame rail by the subframe bolts
This is engineering wise a strong design but does not meet ADR requirements
The way in which the LS1 etc mounts are made would be very much the same to how some 302 mounts would look
Some of the better designs which are ADR compliant look like this
And mount like this