If you are looking to put a H16 frame on a H14, you will probably not be happy with the result. It has been tried before and the boat performance goes way down. When you widen the beam on the 14, you will experience increased tendency to pitch pole and you will have a heavier boat. Basically, when you start to fly a hull, the leeward hull would submerge.
However, to answer your questions, the corner castings are the same, but the H16 probably has bigger holes drilled in them for the bolt that attaches them to the pylons. The side rails are the same extrusion, but longer on the 16 and you would have to install chainplates on them to attach the shrouds on a 14. The tramp for a 16 is much bigger, but you can put a 14 tramp on a 16. You will have a VERY wide gap between pieces, though. I did that last year for a race because I didn't have a tramp for a 16. I ended up weaving a 'seat' between the rear lacing so I wouldn't fall through. If you do install the 16 front and rear beam to widen the beam, you can still use the 14 tramp, but the gap in the middle will be pretty big.
I think the 16 is about 6 inches wider than the 14 and the pylons are about a foot farther apart on the 16.