After crawling around in my attic and crawl space yesterday and inspecting the current linesets for the two units I'm about to replace, I've decided that I'm NOT going to re-use them. There are several couplings, and by the look of things the guy who installed the current condensing units in the 80's only used insulation on the lines where it would be visible--as soon as the linesets get to the crawl space, there's no insulation until just before they exit to the outdoors. Considering that leaks in my old lineset are non-warranty items, I'm not chancing it.
The best route for the replacements is through the attic, which is hot as fire in the peak of summer. Would there be much loss of efficiency from running the linesets through a hot attic?