Tod,
If you have enough material length, make the ramps part of the main bridge beam. Put the taper up, again add a 1/4x2 piece to tie the ears together and give you a surface to bolt decking to.
You may just have done it today Dave - Thanks!
Todd,
Don't you have some marine ply laying around? Just make (4) 12" sq. x 60" lg logs and fill with 2 part expandable foam. Place float logs every 3.5' across the creek and secure with 3/8" poly rope. Lay your decking long ways across the floats and drive your tractor across.