I Found this little note. Apologies to the original poster as I don't remember where it came from. I think they used to post as Snagger.
A 12J or 19J can use the lhs engine and chassis mounts from a 2.25 with no alterations, but you must use the 12J/19J rhs bracket and mount to clear the injection pump. The 200Tdi can use the 109's orignial mountings and brackets on both sides.
All three options will require a custom exhaust, even the 12J, as they need a 2" bore for the nad and a 2.25" bore for the turbo charged engines.
You will not be able to use a Discovery 200Tdi engine in a 109 unless you fit it with Defender manifolds, turbo and oil dip-stick (as I did). The timing cases are different, but this will not matter. 88s will accept the Discovery manifolds and turbo.
A Discovery Tdi will need an electric fan, though the other options can use a fixed SIII diesel fan or, if you move the rad forwards, the viscous fan associated with that engine.
In all cases, the battery tray will need removal due to the injection pump, and you'll have to find another method of fitting the air filter. Oil bath filters are a bad idea with turbo engines.
Both turbo engine will need an oil cooler. The TD can just about get by with a mint SIII export model 4-row rad if it's in perfect condition, but a Tdi should have its own rad fitted.
The 12J and 19J will mate to a Series III gear box with one stud removes and using the SIII clutch parts. A Tdi needs minor alterations to the flywheel housing in order to mate to the bell housing, but the internals all match if you use the SIII clutch, again.
Plumbing the rad to a 12 or 19J is simple - use the top of the SIII thermostat housing and conect to the 4-row rad with standard SIII hoses (top and bottom). The Tdi will need a bit more creativity to mount and connect the rad.
The earlier sections in my blog show the fitting of the 12J, which would match the 19J, in my 109 with a standard 4cyl engine bay. The latest sections show my method of fitting a 200Tdi, including many of the problems along the way, with significant changes to the bay, making use of the Defender front end.
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My 12j cost me £60 and has run for 7 years used most days. I like them. Probably a bit gutless in the 109 but still better than the 2.25. I get between 23 and 25 mpg.
I will get some pictures when I can. I don't think mine is fitted as the above instructions.
Billy