bluegrass
The small difference in thread length is of no consequence.
Most important is the state of the threads.
So long as they are screwed up sufficiently to allow the lower trunnion pin to fit between the swivel lower threads and turn adequately without fouling either the upper or lower swivel threads you will be alright.
Pack well with grease before assembly and fit a set of Declan's new poly seals.
Phil
As above - there's only one thread difference in each 'half'. Just check there is no 'debris' in the trunnion before you screw it on - and when it's one thread from the top - is there any wobble/looseness on the thread?