Hi. I might have some bits and pieces for you. Your story rang a bell, but not sure why. I may have been in contact with other Michigan Pralls that tie in.
The Soc. Sec. Death index has Wm. M. Prall - b. 2 Oct 1921 - d. 11 Nov 1991 Mich.
I found William [b. 1921/2 Mich.] in Detroit in 1930 with mother Iva M. [b. 1880/81 in Ind.], brother Lane D. [b. 1906/7 Ind.], sister Elizabeth O. [b. 1920/1 Mich.]Iva was listed as a widow.
1920 Royal Oak, Mich. - William E. [b. 1877/8 Ind.], Ivy [b. 1880/1 Ind.], son Wayne [b. 1906/7 Ind.] step-son C.R. Duncan [b. 1898/9 Ind]
1910 - Cass Co., IN - Maud Prall [age fits, widowed] with sons Robert [b. 1898/9 Ind.] & Wayne [b. 1906/7 Ind.]
Guessing here: William E. was your William M.'s father. Maud was Iva Maude. William had a brother [Wayne - Lane probably an error] and sister Elizabeth, & a step brother C.R. [Robert] Duncan. Since Wayne and Robert are her sons in 1910, that fits.
Papa was out of the picture during the 19-teens, but back from 1920-??, and gone again by 1930. Due to his "taking off", Maude called herself a widow.
I would tend to think that Wm. E. didn't have a family in Fla. unless he married someone 20 yrs. his junior. He'd have been 52 in 1930.
Wayne died in Oakland Co., MI. You may have cousins from him. Possibly Elizabeth as well.
As for J.W. that could be tricky without knowing what J.W. stands for.
I can do some more digging. Wm. E. had to be somewhere in 1910 & 1930. If J.W. engraved the box in 1903 Cal., then he could well be there in 1900. Do you have access to Ancestry.com?
Terry Prall Pres. Prall Family Assoc. email@example.com