Littlewoods backing started around the time Shankley joined Liverpool so 1959/1960. They were a run down 2nd division club who then started to buy some of the best players around. This was done by huge investment not organic growth. It continued until their period of domination when part of their philosophy is to buy the best players of other clubs to weaken them even though they would play in the reserves. Some did make it to the 1st team.
Liverpool were lucky that this coincided with the abolition of the maximum wage when winning meant more gate and prize money so once established few could compete. Apart from football pools and on course betting on horses, gambling was largely illegal. Most households had a flutter on the pools as it was at a time of post war austerity, it was the only chance of a dream win. Think of the betting industry and lotteries now to understand the relative wealth of the Moores family with Littlewoods the largest with Liverpool based Vernons a poor second in size. They had wealth and could offer wages and transfer fees few if any others could match. No FFP or scrutiny of accounts at that time.
Ironic how this has been airbrushed and how Everton changed from the Millionnaires Club to the self proclaimed Peoples Club, their decline in line with losing pool money support.
I was just doing a bit of research and looking at some of the signings Liverpool made over the 5 year period 1967-72:
Ray Clemence £18,000 (1967)
Emlyn Hughes £67,000 (1967)
Tony Hateley £96,000 (1967)
Alec Lindsay £67,000 (1969)
Larry Lloyd £50,000 (1969)
Alun Evans £110,000 (1968 - British record for a teenager).
John Toshack £111,000 (1970)
Jack Whitham £57,000 ((1970)
Kevin Keegan £35,000 (1971)
Peter Cormack £110,000 (1972).
That's a real significant and sustained investment by the standards of that time and laid the platform for their success in the 70s.
