This shouldn't be a hard beer to brew, getting it to taste similar to the real stuff is where the difficulties are. Your first recipe looks pretty good actually, although there are some changes I would suggest. First, the yeast you want for this beer is WY1318 London III, as it is the Boddies yeast and it will give the beer a slight residual sweetness without it under attenuating. This is key. Also, I would consider using a 25 or 35L British crystal malt instead of the 55L, as the former will give you more toffee flavors than the darker stuff. Also, I would increase the amount of crystal closer to 5-8%, if you do use the 25-35L. The amount of black malt looks spot on.
As for hopping, you can simplify the hop additions greatly, as your mostly looking for a soft bitterness and maybe a touch of aroma. A simple 60 min and flameout addition would be fine, for around 18-22 IBU ideally. Fuggles and EKG would work great.
While the invert syrup would be fine, it really isn't needed and I would just skip it and add a 1/2lb more base malt. 5% sugar isn't going to have much of any impact on the flavor. However, subbing that for Lyles Golden Syrup would be nice, if you are so inclined.
Lastly, regardless of yeast choice (especially with 1318 though) be sure you pitch the yeast at a lower temp (62-64F) and don't let the ferment temp get much higher than 68F. You don't want the yeast to produce a lot of fruity esters.
Good luck with the brew.