Had a similar issue with a chariot head on cub cylinders going on extremely tight. Both american made. Was talking to cam on the phone ordering parts when i had this happen. He pointed out that i had the studs in to deep. Loosened them up and realized they dont turn perfectly true. He told me they dont bottom out and to lock tight them in at the required height. When i did that head slipped right on.
Op, could you screw the studs in while the head is on?