Just fired up DouglasIRIS (4D/25) on the 4.0.5 disk, and it looks like the IRIX4 "cross compilation environment" (even tho' its not a "cross compiler", I'm not sure what else to call it.) from IDO-5.3 will run under IRIX 4.0.5. This is just basic tests (untar it, run "cc" and some other stuff and see if it dies or not), but it looks promising. All I need to do is sort out where everything goes under IRIX 4, and test it on some real source.