Lightweight as in physical or electronic terms???
Your request is rather broad requirement so I'll give you a rather broad answer.
There are many types.
Basic transistor assist for use with kettering coil system.
Then the others.........CDI, TCI
The latter get rather involved even for me at times so I doubt you could handle the understanding (given your opening admission) as it even gives my poor old noggin a work out.
They are out there though in many different forms and in many forums.
The reason I state the difficulty for you is most are
not written with a home builder with little electronics or programming or engine theory in mind. One must, at most times, follow the flow of discussions, disregarding the nong-heads and their comments as the projects are open source and as such open to every tom Dick and Harry to comment.
Reading back can be a task as some go to the hundreds of pages with improvements or deletions, sometimes they just plain run out of steam.
Other than that one could assume and just show you a ready built unit for twins.
The application is model engines around 30-50cc but should not make much difference as the larger engines(if that is your intent) should be a bit lower compression anyhow.
Basically though you would have to suck it and see I guess.
https://hobbyking.com/en_us/replacement-cdi-ignition-for-ftl-twin-engines.html
For a bit of specs data on the single cylinder type (nothing shown for the twin) , go to the address below and hit on "files"
https://hobbyking.com/en_us/replacement-cdi-ignition-for-ftl-engines.html