To reiterate, there is no IDPF for your Uncle Dick. His brother, Bob, in the course of his military service, may have learned of certain records and may have accessed these records but it's unlikely the records would be very specific as to details of his death. Depending on when he accessed these records (i. e., prior or subsequent to the early 1970's) it's possible they no longer exist. Given the logistical capabilities developed by the summer of 1944, it's highly unlikely he (Dick) would have been buried at sea. Again, family stories must always be taken with the proverbial "grain of salt".
Fort Riley, near Junction City, Kansas, is - and always has been - a military installation. The Army and the Veterans Administration have always been separate entities. Inasmuch as he didn't survive the war and the VA deals with veterans, the VA would have no medical records on your uncle.