Remove your new fore stock and reinstall the trigger guard, bushing/collar and trigger guard screws and test your trigger. The thickness of the wood between the bottom of the receiver and the trigger guard has a plus and minus range. If the wood is too thick it will change the angle of the trigger guard and it will be too high. An older fore stock with wood crush will make the trigger guard too low. This is the reason the trigger was moved on the Mk.2 to prevent the trigger from binding or be out of adjustment range due to the trigger guard angle.
With the fore stock installed and the rear trigger guard screw in place the trigger guard should drop/fall into place and be touching the bushing/collar. If downward force is needed to make the trigger guard touch the bushing/collar you have wood binding the trigger guard and it must be removed.
This can also be caused by the wood being too tight in the draws area and the rear of the stock not dropping down far enough and not being in the correct position. (rear of stock is too high)
Is the "new" fore stock brand new and never been fitted before or is the "new" stock actually an older used fore stock?
The No.5 has a free floating barrel but bedding points "A" throught "D" still apply.