measure the overall height (thickness top to bottom) of both desired seats. this will show the seat height differences
if you do not have an "aftermarket pre-made seat for swapping" or "aftermarket seat rail easily modified for custom fabrication" -- doing the above mentioned route I did above is the best route
DC5 and FX8 have a similar interior height. measuring both OEM seats with original seat rail & mounting clips from a leveled floor will provide relative final seat fitness
now flip the seats over to visually see where and how the mounting clips align
cut a thick piece of cardboard or thin plywood to the shape needed and drill 4-holes to mount it to the seat rail mounting clips, then check one with the other
this mock up will tell you how off-center the seat rail mounting clips from DC5 will be if the FX8 seats with OEM seat rails
if the centerline alignment is off more than 1/8", I would not do it. In the event of a serious crash, there is a very good chance the "new welds you just did" will fail. Maybe not the weld bead, but the seat railing stock metal will crack/break-away from the weld bead.
reason for this is the thickness of the metal chosen to make those rails is poor quality. the shape gives it it's strength. When cutting into a fresh piece of metal after leaving the foundary, depending the direction of cut, the grains (just like wood) can be weakened. Then add the heat from welding a mounting clips to the seat rail, some of the strength properties typically are altered. The weld bead may stay in-tact but break free following the welded area.