I've posted a lot of articles about and by Mastro from early hobby publications dating back to the late 1960s, if they would be of any help. Here are links:
Bill Mastro in the hobby press, 1969-70:
http://net54baseball.com/showthread.php?t=221977
1971: Mastro pays $300 for T206 Plank in auction in The Trader Speaks:
http://net54baseball.com/showthread.php?t=218999
1971 Mastro column in Sports Advertiser's Journal:
http://net54baseball.com/showthread.php?t=220718
1973 Trader Speaks profile of Mastro:
http://net54baseball.com/showthread.php?t=217776
1976 Mastro auctions in Sports Collector's Digest, and Mastro article about Frank Nagy:
http://net54baseball.com/showthread.php?t=218636