Is there a 74HCT03 equivalent I can just replace "as is"
That completely depends on the circuitry. Both in terms of logic levels, signal delays, and transition speeds. 

The 74HCTxxx logic family was precisely designed to be TTL-compatible high-speed CMOS. That is, fast and low-power like the 74HCxxx family but capable of accepting TTL-level outputs from the 74xxx and 74LSxxx families. 

If the circuitry around it is 74HC or 74HCT, it is very likely that it can be substituted by a 74HC or faster component. If it is a different logic family, your mileage might vary.