Allan was drafted three times; 1975 Phillies 23rd round, 1978 Rangers 10th round, and 1979 Orioles 5th round, who he finally signed with. So there was obviously some demand for his services. Strangely enough, his Major League career lasted all of 11 games for the '83 Orioles. He made his debut on June 8th and pitched in his last game on September 13th. He went 4-4 with a 3.47 ERA in those 11 games, 10 of which were starts. And then that was it.
His stats were decent that year so I'm not sure how he didn't latch on with anyone in 1984. I couldn't find anything about it but I can speculate that it was either due to injury or a loss of interest in baseball.