It is this CD that has the mono mix of 'He Aint't Heavy':
www.amazon.co.uk/Very-Best-Hollies/dp/B002JIZSQC/ref=sr_1_3?ie=UTF8&qid=1525114800&sr=8-3&keywords=very+best+of+the+holliesI've just done a search for my track list notes, and found that there's actually quite a lot of rare mono mixes on the CD, including 'Sorry Suzanne', 'On A Carousel', 'Carrie Anne' and 'Listen To Me'.
Disc 1:
1. He Ain t Heavy, He s My Brother (Mono)
2. Bus Stop (Stereo)
3. Sorry Suzanne (Mono)
4. Just One Look (Stereo)
5. Sandy (4th July, Asbury Park) (Stereo)
6. Pay You Back With Interest (Mono)
7. Jennifer Eccles (Stereo)
8. On A Carousel (Mono)
9. (Ain t That) Just Like Me (Mono)
10. Searchin' (Mono)
11. Stay (Stereo)
12. Here I Go Again (Mono)
13. We re Through (Stereo)
14. Yes I Will [Single Version] (Mono)
15. Look Through Any Window (Mono)
16. I ve Got A Way Of My Own (Mono)
17. If I Needed Someone (Mono)
18. I Can t Let Go (Stereo)
19. Stop Stop Stop (Mono)
20. King Midas In Reverse (Stereo)
21. I Can't Tell The Bottom From The Top (Stereo)
22. Long Cool Woman In A Black Dress (Stereo)
23. Gasoline Alley Bred (Stereo)
Disc 2
1. The Air That I Breathe (Stereo)
2. Carrie-Anne (Mono)
3. Dear Eloise (Mono)
4. Wings (Stereo)
5. My Back Pages (Stereo)
6. The Baby (Stereo)
7. Clown (Mono)
8. Honey And Wine (Mono)
9. After The Fox [With Peter Sellers] (Mono)
10. Butterfly (Mono)
11. A Taste Of Honey [1968 remake] (Stereo)
12. Hey Willy (Stereo)
13. The Very Last Day (Mono)
14. Blowin' In The Wind [1969 remake] (Stereo)
15. Something To Live For (Stereo)
16. Boulder To Birmingham (Stereo)
17. Say It Ain t So Jo (Stereo)
18. The Woman I Love (Stereo)
19. Heartbeat (Stereo)
20. The Times They Are A Changin' (Stereo)
21. The Day That Curly Billy Shot Down Crazy Sam McGhee (Stereo)
22. Listen To Me (Mono)
23. I m Alive (Stereo)