If I mouse-over the particle pod, it shows that it can go into dark orange, light green, medium green, and yellow tanks, but if I mouse over any of those tanks it doesn't list the particle pod as possible equipment. The heavy tank is the only one that shows the particle pod as valid equipment.

Sidenote: When playing with Space Exploration, the portable fusion reactor is locked behind Deep Space Science. This makes the heavy tank mk1 uncraftable until very late game as it requires a portable fusion reactor.

Not a bug, but by design as class restriction.
For example, particle cannon is the main gun of medium tank. It would be silly (illogical) to allow such an extra oversized gun on light tank, or as second main gun of medium tank... So only heavy tank or above can use that.
My other gun pods in Schall Gun Pod also has this kind of class restrictions.
When you hover on the equipment in your recipe menu or inventory or tech outcomes, the panel lists what vehicles can take that. So you can avoid crafting what your favourite tank cannot use.

Since my laptop is not friendly with large overhaul mods (including SE), it is very hard for me to run those mods, understand their modified tech tree and to make corresponding changes. So I will NOT actively make my mods compatible to theirs.
If the changes are simple and you have lists of all required replacements (tech and ingredients with their internal names, for example), please suggest them here. I will see what I can do with that.
BUT if the changes are too complicated (such as tons of fundamental changes in Industrial Revolution...), I may need to give up, because I do not want to publish something that I cannot test and maintain.

The bug is that the Particle Pod tooltip shows all sorts of tanks as being able to support it. As opposed to the tanks which don't show it as placeable. I can accept that it's not valid placement, but it seems odd that the tooltip suggest its valid. Note that the tooltip does already limit the number of tanks it shows, as it does not display the flame tank for example.

For making the mod work with Space Exploration, I would recommend swapping the fusion reactor requirement with a a vehicle fuel cell. Tier 2 for the heavy, tier 3 for the super heavy.

The tooltip lists are correctly showing what Particle Beam Pods and Particle Cannon Pods can be used, in my game 0.17.75.
I have just tested and confirmed Particle Beam Pods can be used on Flame Tanks, while Particle Cannon Pods cannot. Both are correctly displayed in tooltips.
Can you be more specific which particle pod and which tank class combo that the tooltip is wrong?

I have to think more for the swapping of the fusion reactor equipment in recipes.

Here's what my Particle Cannon Pod tooltip looks like. I highlighted the tanks that it says can take the pod as equipment, but these ones don't actually support it:

https://cdn.discordapp.com/attachments/306402592265732098/641120990180540416/unknown.png

There is no such problem on my end. Those highlighted tanks can use that.

I guess that's a misunderstanding on my part. I interpreted those icons as the light particle tank, medium particle tank and I didn't know what the yellow ones were.

Might I recommend adding an additional sub-icon to represent light/medium/heavy/superheavy?

In general, class restrictions on my equipment are preventing them to install on lighter chassis. The heavier the chassis, the more "room" it has to use those more powerful equipment. Thus, the allowance order is always like civilian vehicle (car) < light tank < medium tank < heavy tank < superheavy tank = mega particle beam tank.
Maybe I will add the class restriction text of the pods (like what I did to Schall Gun Pod) in the technology description next.

I am open to adding sub-icon. But notice that the icon size is only 32×32. It can show very basic ones like the roman numerals (I, II, III), which can still be clear. Not for the more complex ones, they will be a lump of mess that would be very hard to be distinguished.
Maybe you have noticed that I used the military style sub-icon in the tank technologies icons (128×128). But it is impossible to resize them into small icons. That was the reason why I used tinting/shading in item icons upon mod creation.

I've found icons on https://game-icons.net to generally work well as I used these icons in Bot Servicing and they seem to render well at 16x16.

Just released Schall Tank Platoon 0.17.11 and Schall Alien Tech 0.17.13, that fusion reactor equipment is no longer needed in ingredients of MK1 tanks. Now changed to processing unit (not engine).

Looks good, thanks!