I have the same dilemna with my 54. The weight on the VIN says it's a heavier truck. Plus it has a newer engine.
Judging by your wheelbase, I'm going to say it's a 3600 truck. The 3800's were alot longer.
Your engine doesn't appear to be stock. The orange paint gives it away. Not to mention the air filter and aftermarket oil filter.
Good luck with her.
