Slot Expander:Will this work?

Great to know, thanks.

Would it be possible to replace the 74ls352 with a 74ls153 and then invert the outputs (with a 7404)?

Seems the 352 is difficult to find...

and must all the chips be LS or could HCT be used?

I think you can use LS153 without LS04 if you invert SLTSL order.

Yes

Yes, tested and approuved

In general, busdir is used only if you add buffers to the expander. This diagram has only the major functional circuitry of a slot expander, aka the memory control circuitry. Your logic which controls busdir is right but it's only required if you have the intention of adding a data bus buffer to it (so it can control bus direction properly when there are accesses specific to the slot. Because IORQ acesses are "broadcasted" through the whole machine, we have it only turn the buffer inwards to the MSX buffer if one of the cartridges in it turn the busdir signal low during a read cycle. The expander is supposed to do it on it's own when there's a read cycle and it's own /SLTSEL signal is low.

You can add a 4 input AND port to make four BUSDIR inputs and connect the output to the MSX connected side of the slot expander. Ademir Carchano's mini slot expander uses a 4 input AND made of diodes and resistor (DTL logic) so it doesn't need a full 4 inputs AND TTL IC.