I have an intermittent no-start because of no-spark. I replaced the pickup coil. Everything tests fine with a multi-meter, even when it won't start. I don't want to spend the $ on a new ignition module without knowing that's the problem. I also don't want to spend several hundred $ on an engine wiring harness without knowing that's the problem.

I am thinking about switching to aftermarket ignition. I first saw a Mallory unit on ebay that would use the signal from my original pickup coil and fire the coil, which is all I need. But it went higher than I wanted to pay.

Then I saw this Pertronix gizmo that doesn't even require an ignition box, but there is no application for my 1981 245. So will I have to acquire an older points distributor in order to make a Pertronix electronic ignition work?

In the UK there is an after-market electronic ignition system called "Luminition".
It uses a points-based distributor as the starting point, but you pull out all the points components and replace with a 4-vaned plastc disk. This interupts a beam of light, and sends the signal to a special unit, which in turn fires the (traditional) coil. I have used one on several different cars, including a Volvo 240, with impressive results. It improves starting and general running, reduces any tendency to pink on lower-grade petrol, and never needs maintenance or adjustment.
It is well-regarded by UK classic car enthusiasts.
I don't know whether you have this product, but there must be something similar.

That's what the Pertronix is (not light-based, but has a magnetic trigger that fires the coil without an external box.)

I just need a points distributor because it won't work with an electronic ignition distributor without substantial modification.

You won't need an *older* distro, just one with points.

'81 canadian cars came with carbs and points, maybe you can get one of those.
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'73 142, '75 242, '75 245, '80 245, '83 244, '86 244, '87 745T, 92 244 (for sale)

A Canadian distributor may be harder to come by than an older one. 1978 and earlier had points. There are a few 1977 distributors at a junkyard an hour away for $45. Would those swap into my '81?

NO 240 ***EVER*** sold (legitamately) in the US had a points-type distributor.
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'73 142, '75 242, '75 245, '80 245, '83 244, '86 244, '87 745T, 92 244 (for sale)