Just did what Kalpak should have done - looked at the datasheet. Indeed the 89C52BP is intended for driving CMOS only, the Voh is specified at a current of 30 uA.
Thus it is, obviously, necessary to use pullups in a circuit like Kalpaks.

There was a similar post a week or two ago and again, the reason they are called derivatives, not clones is that such parametres will vary from derivative to derivative.

Yes, it is unpleasant that older derivatives are discontinued, but such is life.

Erik