I don't know about the 550's but I have yet to find a "complete" gasket set for the 750. Athena includes some seals that Vesrah doesn't and visa versa. Neither one is "complete" and some seals still have to be ordered from Honda. Also there are a number of internal and external seals for the bottom end that are not included in either(Shifter,crank, main oil,tach drive etc..)
Would be nice if you could get an entire engine package. Let us know what ya find