Any sources for philly jack obriens thoughts on opponents??

I know Philadelphia Jack sparred with both Jem Mace and Joe Louis which is pretty staggering in itself - and i know he worked with and sparred with The Great Harry Greb aswell - and it got me thinking? are there any sources for interviews where he gives his opinions/comparisons between any of the guys he shared a ring with?? I mean when you couple with the above names the fact he also mixed it with Jack Johnson, Sam Langford, sparred with Gene Tunney also, and also fought the likes of Stanley Ketchel, Bob Fitzsimmons, Tommy burns, Marvin hart, Joe Choynski, Jim Driscoll, Barbados Joe Walcott, Kid McCoy, Tommy Ryan, Dixie Kid Kid etc amongst a host of others - that is some experience right there!!? Did he ever give his opinions on those guys and how they compared??

 

Any follow ups on this...?? Interested to find out how they compared in the eyes of someone who mixed it with the lot - surely his views must've been sort after at some point??