Mock up tailgate post to rear floor crossrail

[sterry]

I'm trying to mock up my tailgate posts to the rear floor crossrail. There is more than 1/8" of front to back play between the 2 parts. It would be nice to be able to weld the posts on both the front and the back of the crossrail, but that is impossible as it is now. I can weld some flat stock on the crossrail so that I can weld both front and back, but I'm not sure whether I should be pushing the post all the way forward, or all the way back to get it into the correct position. I guess I will have mock up the whole back end and see which way works best, but was wondering if anyone else might know which way would be considered correct??? Thanks! Scott