Change of engine

Hi,
The vehicle: LR OneTen, 3,5 V8, 1988.

I am considering t get some more muscle and have my eyes set on a larger engine. 4.0 or 4.9.
For once I will pay somebody to do it (my wife is getting seriously tired of me and my LR).
My questions:
1) If I switch to a 4.9 from my present 3.5 (and a LT85 gearbox), which other changes should be done?
2) Could I have something done to my present 3.5 in order to improve it? (I know something could be done, but what would be the best thing).
3) Can anybody recommend a workshop for this? (anywhere in NW Europe (including UK)).

Thks
Ken

4.6 with hotwire injection throw the lt85 box as it will not take the power of the 4.6 also upgrade the back brakes to disc's the r380 box from a disco and a disco tranfere box will make a excellent upgrade done the conversion before works very well.

Many thanks.