Does the recommended book "A Retargetable Compiler for C..." provide
up to date information if you are interested in creating a backend?

Is the technical report, "The lcc 4.x Code-Generation Interface", what
I should be digging into (in addition to the code, of course)?

Also, if there is other reading materials or tutorials available
please point me in the right direction.

So far I can build lcc 4.2 from source and get it to generate asm code
for the provided targets.

Kindly,
graham

...
The technical report provides reasonable information if you already
know the compiler internals.  I've read through it several times.  The
next step seems to be to work through the existing back-ends.