Alternative HDD technologies are a no go, they don't even work on later 386/486 Compaq systems.

Being a 286, you might get away with running the system from floppies alone, unless you want to run a windows based OS or programs larger than 1.5Mb.

I second that. I once had got a Compaq SLT286, too. Compaq was quite proprietary in its golden days,
which was both good (first 386 PC) and "bad" (special SIMM modules; PCs which required special boot disks for BIOS access etc).
As far as HDDs are concerned, a Compaq PC can be a little bit cumbersome, comparable to Toshiba´which had hard-coded HDD entries I think.
Provided that you find another HDD with a compatible wiring, you perhaps need a special floppy with the CMOS utility in order to alter HDD settings.
Maybe a generic PC/AT utility for DOS also works, not sure. If you've got the floppy, have a look at the HDD part first and check
which HDDs are supported.

For the case you've got an electrically compatible HDD that's not supported, you have several choices, I guess.
a) Select a smaller HDD (smaller in capacity) that is within the specs
b) try a disk drive overlay software (DDO) that works with 286 processors
c) use XTIDE somehow (use an eprom reader to backup the BIOS, then combine the dump with XTIDE and write it back to another EPROM)

Sorry, that's all that comes to my mind right now. If I still had my 286SLT, I could double check what I wrote. 🙁

Ok, thanks for your replys!