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That is my car in the referenced Swedespeed thread.
Column mount electric power steering units are now ubiquitous, not just in Asian cars. GM / Saturn were / have been using column EPS units for probably 20 years. The GM Opel was probably the first common donor for EPS retrofits. If you are going to troll the pick and pull looking for a donor, I advise that you select an EPS unit that has an operation mode where the EPS defaults to a minimum assist if it does not have a vehicle speed signal. Specific versions of the Nissan Versa and the Toyota Prius meet that requirement. There may be others if you are prepared to do your research. The GM units required a speed signal which most people created by adding an adjustable pulse generator to fake a speed signal. On more recent cars which typically use CAN bus communication systems that is much more difficult to do so make sure that any unit you pick will operate without the speed signal unless you want to get into firmware coding.
Aside from having a minimum assist default mode, the other factor is 'fit'. Five - six years ago the Versa and Prius were the common donors. The drive motor on the power unit on the Versa is clocked 180 deg relative to the Prius. Unless you were going to mount the drive unit with the motor hanging straight down, the Prius unit would not fit on a 140 as the end of the drive motor would hit the heater housing. Hanging the drive motor straight down is an option if you have a vehicle with a lot of clearance in the footwell under the dash. On my 140 the drive motor hit the lower valence and I wanted the vehicle to look 'correct' so removing the valence was not an option. On the 1800 I expect the footwell is tight enough that the drive motor would interfere with your feet if you hung it straight down. I found pictures of the various EPS drive units on the web and scaled them and then got under the dash to try and figure out what would fit.
I scored my Versa EPS unit from a pick and pull. I actually removed the complete upper part of the steering column from the car which included the drive unit and the electronic controller. The salvage yard had a flat rate for steering columns which was cheap with the only distinction being adjustable / non adjustable. They did not distinguish between EPS and non EPS units. I think that particular ship may have sailed as they have probably figured out that the EPS equipped units have a lot more value. If you think you can source an EPS unit for $40, make sure that you are getting both the controller and the power unit.
It occurred to me that my installation 'might' have been easier if I had taken the
Versa steering wheel and column covers and just transplanted the complete upper part of the Versa column into the 140. This would have given me an adjustable steering column with a collapsible top end section and avoided a lot of the top end machine work with just a need to interface the Versa output to the Volvo steering box. However, it definitely would not have looked Volvo.
Picking up an EPS unit from a salvage yard is not going to make for a simple bolt in installation. There is a reason that the EZ installations are not cheap; but, if you want something that you know will work they are the way to go.
https://drivenman.com/product/volvo-p1800-s-e-es-ez-electric-power-steering-fits-with-factory-a-c/
I believe that the EZ units use the Corsa style power unit.
Some people have complained about loss of steering feel at highway speeds with EPS. Part of that problem is that the Volvos of this vintage had very little steering caster. Caster generates self centering steering action once the car is moving; but, makes the steering heavy when the vehicle is moving slowly. Volvo skimped on the caster to make the cars easier to steer and relied on stiff steering to provide feel. With EPS you loose the 'stiff' effect which means the steering is very sensitive to pressure on the steering wheel and you can end up in constant correction mode at highway speeds. If your steering box and tie rods have any slop in them, this will just exacerbate the problem. I was going to experiment with a speed signal for the Versa unit which was going to be a fair amount of work because it required programming on the CAN bus. However, before I did that I did a little fiddling with alignment. On the 140 Volvo specified 0 to +1 deg caster. I adjusted the alignment shims to give me about -.5 deg camber and +1.65 deg (L) +1.8 deg(R) caster. Modern cars with power steering commonly run up to +5 deg caster. The increase in caster definitely improved tracking at highway speeds. If I get motivated to crawl under the car again to try and balance the L/R caster on the wheels I may try cranking them both up to the + 2.0 degree range. With the change in caster I am now disinclined to bother with fiddling with a speed signal.
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