I took some blow up's of the Riquimbili and tweeked the image so it can be seen better and analyzed. I've looked at it closely and noticed:

1) no bicycle pedals

2) a rubber drive belt for the primary from the motor which looks like it came off a old washing machine.

3) the secondary chain drive to the rear axle slants downward on the top side.
what looks like the upper chain is a brake lever connected to a brake pedal on the left side

4) behind the larger primary rubber pully drive is a small sprocket connected to the larger rear sprocket.

5) to the sides of the rear swing arm suspension there are built out foot rest like running boards on the old motor cycles. so the rider's feet rest aft of the center of the bike before the rear axle.

6) it isn't clear if the front suspension is articulated or just relies on the springing of the long extended raked forks.

7) it appears to only have a rear brake possibly from a small motorcycle which may also be where the rear brake rod & pedal, and spring loaded shocks were
salvaged from. Likewise the throttle grip and cable (notice the long length of cable) I'm not shure if bicycle parts were used in this or to what extent but the front forks look like they could have came from a small displacement motorcycle. thus this bike could be a massive rebuild of a small motorbike frame.

The smaller blow up of the pedal crank & primary pully/front sprocket gives some better detailed view for your analysis.





I haven't gotten to trying to calculate the pully diameters by "guesstimation"
in order to convert engine rpm to feet in forward movement yet but I'm sure these things move along and only sip gasoline which must be expensive in Cuba.

So, enjoy the view !