It is worth bearing in mind that guitar construction in the 20's, 30's, 40's, was much heavier than is currently fashionable. This was a two-way thing in as much as they were built to withstand the enormous tension created by heavy gauge strings which were the only type available and you needed heavy strings to get volume and a decent tone and projection from instruments built like battleships. Tricks of the trade for blues guitarists included tuning down lower than concert pitch to make it easier to fret the strings with the fingers and to allow string bending. Also using a standard set of strings and discarding the lowest one or two (5th & 6th) and shunting the remainder down so what was a 4th string would take the place of the 6th and so on and using plain banjo strings for the top two (2nd & 1st)This was common practice here in the UK in the 50's after Rock & Roll first hit which was before light gauge strings were sold. Those old blues guys used to use cheap mail-order guitars and to get any sound out them at all you had to whack them pretty hard, it is testimony to their skills that they made them sound so good. I don't advise stringing a modern accoustic guitar with really heavy strings unless you tune down a good way otherwise you'll be in danger of the strings pulling your instrument apart. (.070" gauge? Wow!)