I managed to borrow the tape from my guitar club friend and I figured out the chords on my guitar.
This may be slightly different than the original but it sounds right to me.
Wonderful song......

    D                                           A
He picked up the picture and smiled as he said,
         D                         A --E
"I was a handsome devil back then,
      D                                    A
But it's been so long, just so many years,
       D                      E
That I can't remember when.
D                         A
When I was a young lad so dashing and proud,
D                              A --E
I used to play this here guitar.
       D                               A
All the pretty young girls would gather 'round me
    D                               E
As I sang about love and the stars.
    D                            E
But life has a way of changing things,
    D                                     A
And it's done its cruel number on me.
    D                                  A
But though my hands are crippled with age,
D                                    E
I live by this phil-oso-phy:

Chorus: (Play 2 times).
A                               E
When I can't play, I'll sing.
D
When I can't sing, I'll whistle.
A                                        E
And when the day comes I can't whistle no more,
    D          E                           A
I'll sit myself down and I'll listen.

Oh, oh, when I can't play, I'll sing.
When I can't sing, I'll whistle.
And when the day comes I can't whistle no more,
I'll sit myself down and I'll listen.

      D                                           A
Well, I haven't seen him for a number of years,
D                                       A --E
But it always comes into my mind,
       D                                           A
When I struggle, I think, that I'll give up the ghost,
      D                                     E
These few words that he left behind:

Chorus: When I can't sing... (play twice)