Just posting the facts to help others, all bits came from Johnny.
Bafang Mid-Drive 1kW, 68mm, no motor spacers used.
42T Lekkie Bling Chainring is best for alignment, it comes with one spacer, two are required for this bike. This puts the chainring really close to the frame, but seems OK after a few spirited rides. You can stack three Lekkie spacers in there to be safe but you will lose the lowest gear.
Longer chain is needed
Brake sensors do not mount easily due to the shape of the handles so I didn't use them. They aren't required by the controller.
Speed Sensor and Shift Sensor are easy to install
52V 17.8 AH Super Shark Battery fits fine in the triangle
The right pedal is a few tenths of an inch further out than the left, would require an offset crank to fix, but it isn't noticeable for my fishing bike.
All 10 gears are usable.
Only install issue I had was the thread machining on the Bafang drive shaft was offset from center which created a lip around half of it so it wouldn't fit into the BB, had to spend an hour with a die grinder adjusting my frame, should have sent it back to Johnny but I'm impatient. Hopefully your motor casing is better machined.
After some programming I find this setup hauls butt even with 28 Amp max the controller is hard coded for. Only change I plan to make is perhaps a twist throttle.
Party On,
Joe
The only real problem I had on mine was burrs inside the tube where the motor shaft goes. filing took care of it.
What year is your Marlin 6? I have a 2018 Marlin 6 and looking to turn it into an ebike.