I gave up waiting for MMC to have them in stock so went to S-V-C who had just taken delivery and assured me that their Lucas copies were good quality so I took the plunge. My original Wipac's had the sidelights fitted within the lamp bowl so this meant that S-V-C would need a drill the Lucas bowls and supply a side light fitting - a service that is offered on their website so I paid for them to do that as well.
Now hindsight is a wonderful thing and with that benefit I would have removed the original lights and had a poke around to find out what's what before ordering. However I didn't so when asked the question 'where do you want the side lights fitting' I went by the Tribar pictures on the MMC website and said at a midpoint between the headlamp bulb aperture and the edge of the reflector bowl

The lights eventually arrived and I was a little disappointed to find that one of them had some sort of film or mist on the inside of the lens. Arrangements were made to send it back. In the mean time I did what I should have done from the off and removed on of the original headlamps and dry fitted the remaining good Lucas.
You can see the difference in sidelight location straight away:
This caused a problem because the W5 bulb holder supplied by S-V-C fouled the plastic headlamp black plastic nests fitted in the wing recess and put an undue amount of strain on the plastic beam adjustment screws. Bugger!
This can be seen where the dust has been rubbed away at the 6 o'clock position (don't worry - it's all been cleaned up in there now

. Then I realised that the original 4W headlamp bulb holder was a perfect fit within the grommet that S-V-C had put in the hole drilled in the Lucas - the problem being it sat outside of the Lucas rubber dust boot and was not covered by the original Wipac one as shown by the black marker pen line in the top photo.
So I took photo's and measurements and contacted S-V-C knowing the that faulty light unit had not yet been delivered back to them. The plan was that they would hopefully drill the replacement lamp as per the photo and I would have to stump up for one more unit. An expensive mistake but the bonus would be that I wouldn't have to mess around with the wiring and they would effectively be 'plug and play'.
Having phoned S-V-C and explained the problem they readily agreed to drill the replacement as per my photo and to my delight and surprise, agreed to send a second lamp similarly drilled free of charge. Fantastic service

So fitment day was yesterday. I ended up having to carefully trim down the red shroud around the wire (as below) to 2mm because it's original length caused the dust boot to sit proud of the reflector bowl but once done, the boot was a snug fit. There is also plenty of clearance between the sidelight build and H4 headlamp bulb which had been a nagging concern.
So job done and very pleased with the aesthetic results. I've read that these Tribars are not great in terms of light output but I was aware beforehand so went into it with my eyes open.
Before:
After:
