Was just going to say that too Mr Martin. Danny, there are different bell housings available for land rover gearboxes which will dictate the positioning of your engine on the chassis relative to the gearbox. There are a number of chassis' for the Defender eg Turbo Diesel model, 200tdi model, 300tdi model, TD5 model etc, each with a specific set/type of mounting points for gearbox, transfer box and engine. When you start building a hybrid vehicle from the ground up, then you need to consider these mountings. For example - if you fit a 300tdi Disco engine to a Defender Turbo Diesel model chassis (up to 1990), then you need to sheer off the original engine mounts and weld new ones on in order to keep your gearbox in the right place - with quite some precision welding.
Can I suggest, without sounding patronising, you get involved with a local land Rover club or group - it will save you many hours of time, wasted effort, money and frustration as well as keeping you going... I've learnt a lot on here, but a few conversations with an old hand standing in front of a Landy project are valuable indeed.