I see this is your first post! Welcome!
Currently, does your CJ-3A have an engine? It almost sounds like you may not. What about the rest of the drivetrain?
If the company you're corresponding with is state-side, they should absolutely have documentation on the L-head - and its multiple applications. If they are overseas, I'm just going to say, "Buyer Beware." With overseas, you could finally get the engine but may still end up with a pricey boat anchor or still have to spend extra to get it to fit and work.
But to answer,
Pictures are great. The phrase, "A pictures speaks a thousand words," comes to mind.
The Service Manual is great for understanding/repairing but most of the images within are exploded or cutaway. It may be that you'll need some data on the engine from the "Specifications" section, Section D. Have you scoured the 3A page, the 3A info page? You may find some engine images embedded within. Also, there are some images on the CJ2A Forum since they also use the flat-head engine.
An alternative...
It sounds like you don't want to, or can't, do any engine refurbishing. You can get a used engine that may just drop in and run. Or you may find one that is in desperate need of rebuilding.
Having a known CJ3A/CJ2A engine with all the attachments needed to function in your jeep may be worth the trouble - even if it needs rebuilding.
Your post didn't give any insight as to where you intend to go with your project. Some want a 12V conversion with an alternator. Some have even stuffed a 134 F-head under the hood, both with and without cutting the hood.
Share more information including where you're thinking about getting this engine from as well as your general location. Others here may be able to provide you with better intel on where you are and where you want to be, or there may be a nearby neighbor who has a spare engine in the barn.
I mention this as there is a Fall Reunion approaching fast and there was a member on the 2A forum who stated he had 2 spare engines.
Can you post an image of your jeep?
