measurement needed SORTED brain now working

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As my bus had been VERY badly repaired (90s) when I cut , more like pulled !!!!! the sills off and arches and load bay floor I have no measurement for the width of front ( on top of front cross member ) under floor top hat section. That is the width between inside of sills. Its been a few years since doing sills on a bus and (doooo) I forgot its narrower at the front, bought 4 top hat sections from Scofields but they don't seem to list a narrower front one. So if anyone knows or can crawl under a non welded bus and put a tape between the inside of sills I would be grateful.

 

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Had a moment of clarity whilst doing an mot this morning , all I need to do is measure the depth of the sill and take that of the end of cross top hat section. Was over tired after 6 1/2 days cutting and grinding ( some holiday!!!)