[craggle]

3.5 front cover should fit straight on.
Spacer is needed to stop the pulley going too far on the crank.
3.5 sump will fit as long as you have the 3.5 front cover. Spin the engine over to check for crank clearance before starting!
Use a cam shaft that has the space to fit the original 3.5 distributor drive gear on the front and stick with the original distributor. Forget the coil packs.

If you are offered a cheap 4.6 engine ask why. These were only fitted to Range Rovers and they had a habit of getting too hot. Bad fuel maps for economy, small radiators and owners not checking the water level often enough led to overheating. A 4.6 engine is well known for cracked liners or liners that have dropped down the bore slightly allowing cooling water to seep past the liner into the bore. The only permanent fix is to have the block re-sleeved with top hat liners. This can cost more though than buying a new 4.6 short engine from one of the specialist V8 dealers.

Be careful

Craig.