Found this bit of blurb on the subject but i dont know how accurate it is.

Bob

If using the standard Zetec flywheels, you will need the starter motor from any OHC Pinto based Sierra from 1982-1989 or any CVH based Sierra from 1987-1993. This is a Lucas LRS543 or equivalent.

Please be aware that this is available in two variants with different diameter motor housings, one around 3½" in diameter and the other around 5" in diameter. The one with the lager diameter motor housing will not fit and will foul on the sump. Therefore, you will need to specify the smaller diameter model.

Starter cross references
 

A really good guide to starters and fitments . Just click on any numbers in red to get more info. Handy for cross references.

Bob

http://www.woodauto.com/vehicle.aspx

Well I bought a LRS543 from my local motor factors today and it won't fit. The face of the flywheel is about 17mm from the box mating face and the LRS543 would be constantly engaged. Luckily he's got a LRS707 in stock so hopefully I'll swap them over tomorrow

I ordered this starter from work brand new. as you can see i have a 2.0 blacktop with a 1.8 silvertop flywheel. This starter fits a 2.0 sierra with a pinto, because its brand new part with gear reduction design (rather than a rebuilt lucas) It fits a treat. The original starter this replaces would have had a larger diameter motor and fouled the sump.
I would ask your local auto electrician rather than your motor factor as they can look up the exact measurements, mounting hole locations and throw etc

Rich. How far is the flywheel from the box mating face on the blacktop?

Swapped the starter motor today for a LRS707. I'm putting up a pic so people can see the difference. This one looks like the one for 2.0L Mondeo silvertop with 1.8L Escort flywheel.

Hi Gaz

That 707 stater in your latest pictrure has the same measurement as the CVH starter currently removed from my 1.8 Zetec set up.

I still have a Sierra 2 litre DOHC starter here. this also has the same measurement.

It's a minefield Ronnie. I,m guessing the LRS543 is a pinto starter because it would have done if I'd made a 15mm spacer.

Minimal grinding of the sump and the 707 fits perfectly. Wired it to an old battery, took out the plugs (it's got no oil in it) and it spins up luverly.

I've put a small filter on and will fill it with oil tomorrow. I was starting to loose a bit of interest in the car so have set myself the goal of making everything needed to get the engine running.