Hi Tim,
The cocking lever on an LG400 has quite a large off-set to space it away from the stock and I can see from the picture link you supplied that it can clear the scope quite easily.
This is not the case with the LG300 cocking lever which is much closer to the stock and actually hits the underside of the scope during its upward travel during cocking. This is the reason why the cocking lever on the Dominator (LG300) is entirely different.
It looks like it would be much easier to convert an LG400 mechanism to an FT rifle than it is to convert an LG300 mechanism for FT use.
Bob.