I'm going through this right now. I ordered an 89-91 hose, but all of the parts stores I looked at stock the same hose as my stock 85 one:
The short answer is that none of the parts stores carry the A/C hoses for 89-91 square nose (gas) unless you have rear A/C. AC Delco is the only thing on the market.
With the compressor on the right, I worked over my stock lines with a conduit bender to get everything connected, but the return line still has a bit of a twist to it. It looks silly with such long hardlines coming up out of the compressor and stretching about a foot towards the coolant overflow tank. They need to go down from the compressor.
I tried the Camaro lines - the small hose reaches the condenser perfectly, but the large one is too short and bent wrong to reach the accumulator.
The pickup-truck lines have a bend to reach the condenser, whereas the square-nose condenser requires a straight shot here.
RockAuto no longer lists anything related to 15-3867. For 90-91 Blazer, they only show the hoses for "with rear a/c" (yeah, right). This is the only hose set they sell for 89-91 square nose, whether truck, sub, blazer.
Amazon shows it and I believe it to be correct:
I also see it on eBay, but no hits for any other car parts site.