Hi Falcons
Yes, the LT77 (and later R380) are by far the easiest in the UK. You will need everything from the back of the engine on an SD1, or source the same bits separately from other vehicles. ie crank spigot, flywheel, clutch, bellhousing, clutch release mechanism and gearbox. Your existing prop shaft is suitable as is. You will need to shorten the gearlever that comes with the box and make/adapt some brackets for the gearbox rear monting to the car. If the box you buy has a mechanical speedo drive, you will need to buy a suitable speedo cable - these are available off the shelf - and then have your existing speedo recalibrated to suit. If the box has an electronic output there are adaptor sytems to allow the elctronic output to drive your mechanical speedo. Then you need a manual pedal box so that you have a clutch pedal and master cylinder. Depending whether you finish up using one from a P6 3500S, P6 2000/2200 or an SD1 there are then a number of hoops to jump through to allow the pedal to operate the clutch.
Easy Peasy!
Chris