Theres a place in liverpool that might be able to give you a quote on an engine swap that advertise on ebay.

is there no chance the blocked could be refurbished at all and maybe oversize pistons fitted? FFRR MY06 facelift With TDV8 Alloys Zeros/ATR's
Mantec Sump Guard, Rigid Load liner, MY10 BT upgrade.

I've had a few quotes ranging from £2450 to £3500 +vat. I'll be taking one of them, probably the one with the best warranty. If I put in an LR straight swap, will I need to change the ECU and any other electronics or will my existing one do the job?

I should imagine you will keep all you exiting ecus, otherwise it's a pain to get them all talking to each other

The engine only has sensors that will need plugging in.

I'm sure someone will correct my if I'm wrong though