74L can be replace by 74LS, 74 or 74S
74LS can be replaced by 74 or 74S
74 can be replaced by 74S
74S cannot be replaced
not sure about HC, haven't checked a spec sheet, but it only comes down to chip speed and current capacity or fan out ratio. Speed will not be a problem in pins as they are slow. Read the spec sheet for the HC device and compare it to the 74 spec sheet. I've got a feeling they will be ok - I think 74HC were released as a universal replace all series, but check the current rating to be sure.
