Sounds like a cool truck! I am sure I will be happy with my Marlin 1600 and stepped flywheel when I drop in my new motor.
The heavier flywheel just keeps your engine from dieing as quickly as normal when chugging along... something about momentum and stuff.
I am sure the Downey kit will be fine... personally I would do the 1600 lb Marlin clutch. I have a cheapy parts store clutch in it now thats not even a year old, and it is slipping with 30 inch tires, so I decided to go all out when I drop the new motor in.
