Christmas Mission

[DaveyT]

Hello
A recent post describing a brew producing a dark and a light beer (sorry, I forget the author) has inspired me.
I have an 8.5l brew length which reduces down to 7l. If I split this two ways, I'm willing to dilute each 3.5l batch by 100% but not comfortable going above this. So the aim is to produce two beers: 7l and 6l which totals 13l.
So the base brew is:

13litres
OG 1.029
650g Extra Pale DME
350g Wheat DME
44g Fuggles

English Christmas Ale
7l
OG 1.036
250g Crystal malt
50g Chocolate malt
These are to be steeped then boiled separately before adding to FV A.
Then some Christmas pudding dried fruit and spices will be added once fermentation has died down.

Canarian Christmas Ale
6l
OG 1.037
90g golden syrup
20g Brewer's Gold
Both in a pan to make a hop tea to be added to FV B.
Once fermentation has died down an as yet undecided quantity of mandarin marmalade to be added.

Hmmm... Is it doable? Shall I bother?
One issue is I'm not sure what the IBUs are.
I wanted a beer close to the Arkell's Mash Tun Mild recipe I tried last year. An alternative would just be to do it again and not try this experiment.
I hope I've explained this clearly. Apologies if it's confusing. I've just made a stout so I wanted something blond, but then it's about time to think about Christmas.
All comments welcome.

Cheers
David