I have installed an EPS unit on my 1971 142 that I extracted from a salvaged Nissan Versa. If you are interested, the description of the installation starts in post #289 in this thread.
https://www.swedespeed.com/threads/w...age-15#replies
The installation should be similar to any 140 up to the dash change in 1973 (or 1974?). I don't know what changes were made to the steering column, if any, in the post dash change cars. The big wrinkle would be the left hand steer versus right hand steer difference.
The two EPS units I considered for my installation were the Nissan Versa unit and the Toyota Prius unit. The primary benefit of these two systems is that they both get their vehicle speed signal over a CAN bus and if there is a CAN bus failure they default to a base assist mode. Turns out that the base level of assist on the Versa is more than adequate for low speed maneuvers and with a little tweaking to castor angles and a smaller steering wheel is good at highway speeds.
I wanted my EPS installation to be completely out of sight in the interior. This means that the drive motor for the EPS unit has to be positioned horizontally so that it is not exposed below the fascia. Clocking the drive motor vertically is not an option because that real-estate is already used up by other stuff. On my left hand steer car the drive motor is clocked towards the heater because there is insufficient horizontal space between the steering column and the lefts side body sheet metal to fit the drive motor. That dictated the selection of the Versa unit because the Prius drive motor is oriented 180 deg relative to the Versa drive and would not physically fit in the available space. A Versa EPS unit will not fit on a right hand steer car (which might be academic if Nissan Versa's are not available in the UK market). However, the Prius drive motor being mounted in the opposite direction should allow for a mirror image of my installation in a right hand steer car.
If you are OK with the drive unit not being out of sight or are prepared to modify the lower fascia to fit then there may be other drive unit mounting options.
With a 14" steering wheel and running about 1.5 - 2 degrees positive caster the steering assist is close to ideal. I think increasing the caster to around 3 degrees positive might be ideal for highway driving; but, so far it has been good enough that I have not been motivated to go through the process of changing the shims to alter the caster and then resetting the camber. Access to the alignment adjusting shims is not exactly convenient on the 140.
Volvo's answer to no power steering on the 140 was a steering wheel the size of a hula hoop, narrow tires and zero to a tiny bit of positive caster. If you install EPS of any kind I suggest that you ditch the original steering wheel and increase the positive caster, otherwise you will find the steering over assisted at highway speeds and the minimal self centering in the steering caused by Volvo's use of tiny caster angles will make the car prone to wander because of driver input. Increasing the positive toe might be something worth considering; but, I have not experimented with that. Adjusting toe angles is much, much easier than adjusting caster angles; but comes with increased tire wear and a reduction in steering sensitivity.
When I did the EPS installation on my 142, another 142 owner donated a spare steering column and mounting bracket from a salvage car for me to use as a donor for the purpose of cutting and fitting to test the installation. I didn't want to cut up my steering column and mounting bracket only to find out that this was not going to work. The agreement was that I paid for shipping the parts and if this worked out I would provide details on how to do the installation so I ended up creating a fairly detailed installation guide. I think I still have that document on my hard drive so if anybody is interested send me a message with an email that accepts attachments and I will forward it to you (if I can find it). It covers a Versa EPS installation on a left hand steer car; but, a lot of the issues addressed will be similar for a right hand steer car.
As a final observation, I would not get overly obsessed about safety issues with the EPS unit itself. If you have complete failure of the drive unit you just revert to no assist with a tiny bit of additional drag which increases steering effort. If you want to obsess over safety issues I would obsess over Volvo's cheap ass implementation of a collapsible steering column with that offset break away section just above the steering box. After a few years of service the bushings get all wimpy and contribute to lots of steering slop and they have been known to work themselves loose. When I did my installation the Versa steering column came with a collapsible splined lower column which I used to replace the existing Volvo lower column section. The splined column eliminated all the flex associated with the Volvo break away column section.