This is an Transmission 3 speeds add-on for the Ford FlatHead V8 engine.
It's a complex remix of "1939 Ford Toploader Transmission by skipstitch" (https://www.thingiverse.com/thing:2940612).
It is made up of 19 pieces ; the release shaft works and the drive shaft turns on bearings.

Original engine : https://www.myminifactory.com/object/3d-print-106731

My final project :

Print Settings
1 x TransmissionBody : Layer:0.15mm Raft:no Brim:no Support:yes Infill:15%
1 x TransmissionBodyGasket : Layer:0.15mm Raft:no Brim:no Support:no Infill:100%
1 x TransmissionCover1 : Layer:0.15mm Raft:no Brim:no Support:no Infill:20%
1 x TransmissionCover1Gasket : Layer:0.15mm Raft:no Brim:no Support:no Infill:100%
1 x TransmissionCover2 : Layer:0.15mm Raft:no Brim:no Support:no Infill:100%
1 x TransmissionFrontMainDriveBearing : Layer:0.15mm Raft:no Brim:no Support:yes Infill:100%
1 x TransmissionGearShift : Layer:0.15mm Raft:no Brim:no Support:yes Infill:100%
1 x TransmissionKnob : Layer:0.15mm Raft:no Brim:no Support:no Infill:100%
1 x TransmissionLever : Layer:0.15mm Raft:no Brim:no Support:yes Infill:100%
1 x TransmissionMainDriveGear : Layer:0.15mm Raft:no Brim:no Support:yes Infill:80%
1 x TransmissionPurge : Layer:0.15mm Raft:no Brim:no Support:yes Infill:100%
1 x TransmissionPurgeGasket : Layer:0.15mm Raft:no Brim:no Support:no Infill:100%
1 x TransmissionRearTransMounts : Layer:0.15mm Raft:no Brim:no Support:yes Infill:20%
1 x TransmissionReleaseBearingHub : Layer:0.15mm Raft:no Brim:no Support:yes Infill:100%
1 x TransmissionReleaseShaftFork1 : Layer:0.15mm Raft:no Brim:no Support:no Infill:100%
1 x TransmissionReleaseShaftFork2 : Layer:0.15mm Raft:no Brim:no Support:yes Infill:100%
1 x TransmissionReleaseShaftForkLeft : Layer:0.15mm Raft:no Brim:no Support:no Infill:100%
1 x TransmissionReleaseShaftForkRight : Layer:0.15mm Raft:no Brim:no Support:no Infill:100%
1 x TransmissionScrew : Layer:0.15mm Raft:no Brim:no Support:yes Infill:100%

Accessories
4 x 4mmx2mm disk magnet
6 x m3 threaded insert
1 x m3x73mm threaded rod
1 x m3x65mm rod
2 x m3x1mm SHCS (cut m3x3mm)
10 x m3x5mm SHCS
16 x m3x8mm SHCS
1 x m3x5mm set screw
2 x m3 jam nut
3 x m3 washer
2 x 6702zz bearing
2 x 623zz bearing
1 x pencil spring

Assembly
Look at pictures.

More add-ons

https://cults3d.com/en/design-collections/dancan13f/ford-flathead-v8-engine-add-ons