Belt Tensioner on a Drive Belt?
 

I have a Honda FL350 and swapped the engine and bought a commet 94C clutch, the old belt however has to travel a longer distance. The only drive belts that I could find online that were over 50" long with a width of 1 3/16 was a drive belt for a John Deere Gator. This Gator belt was 56" long, is it possible to put a tensioner on the 56" belt in between the clutch and the pulley so that it fits?

Maybe fab up an automotive serpentine belt tensioner?

You could do that, the only way to know if it will affect the way the pulley sheaves react is to try it. Most large mower decks have idler/tensioner pulleys designed for the backside of the belts to run on--just like an automotive type as xlint mentioned. You may have to set it up so that the belt is "squeezed" evenly between two idler pulleys so that it runs with the correct wrap around the clutch and driven pulleys. It may even need to run through 3 pulleys to use up the extra length and still have the belt coming in and out of the drive/driven pulleys on the correct angle.

Thanks I ended up using a spacer on my secondary clutch to accept a wider belt!