When I started racing in the early 60s aero meant riding on the drops. Training consisted of getting the miles in usually on 66 fixed and early season reliability rides.
A close mate of mine was a top-level rider in time trials of the late 50s - a bit before your time, though you might have heard of him (Mick Ward).
His primary training was cycling to work and back. He didn't have a car, so he'd have to cycle to events. Nutrition was whatever food he could afford - there were no energy gels or drinks available or post event massage.
Mick was the first guy to win the National 25 & the 50 in the same year - 1958; he won the 50 in 57 minutes something. In the same year, he came 9th in the 100 and 2nd in the 12 hour, behind Ray Booty. It was only his 2nd ever 12 hour race; in the 100, he had a wheel breakage and he did the last 25 miles on a marshal's bike - couldn't see that happening today.

(He also won the National 50 in 1956 & 1959 and was second in 1957).
Mick has nothing but the utmost admiration for the riders of today . . . . . . . mind you, had he been competing today, I'm sure that he'd still be a top cyclist.
It is always difficult to compare different eras however it is a fair point - Things have changed and if going under the hour for a 25 was once the mark of a strong rider, then IMO that is no longer the case. That doesnt mean it is easy - it is still a decent mark to aim for, just that with developments like tt bars it is now within reach of more riders than in the past, even if they had exactly the same fitness and training (etc) as racers 40 years ago.
In my opinion, ^^^ this reply is accurate.
Apart from the 'obvious' technological developments. riders are much more 'clued up' on issues such as nutrition, training, rest, tapering etc.