Sparky, depending on the magnification you want to work at, you might be better off with a 40/4.5 Luminar or a 45/4.5 Mikrotar or even a 25/3.5 Luminar than with a 55/2.8 MicroNikkor. One guy on the French LF forum insists that a reversed 55/3.5 MicroNikkor shoots better above 1:1 than the f/2.8er. We have a late 3.5er in the house; to my everlasting shame, I've never tried it. If you ever look for a Mikrotar, be very cautious. I've met a couple that wouldn't focus; they were missing an element.
The shorter the lens, the less extension needed to get the magnification. Adapters for holding lenses in RMS thread in front of shutters (#0, #1) used to be fairly easy to find, but I haven't chased 'em for a while. I have mine ... Although my tubby little MicroNikkor edged out two 63/4.5 Luminars (mine and Charlie Barringer's), our 40s beat it at higher magnifications. Adapters to hold a reversed MicroNikkor in front of a shutter are much less expensive. And MicroNikkors are much less expensive than Luminars.
If you need a 25 and can find a clean 25/1.9 Cine Ektar II (clean makes a big difference and many are filthy inside) shot at f/2.8 beats the 25/3.5 Luminar (two examples) above 10:1.
Thinking of which, one thing that many people don't fully appreciate is that real macro lenses are usually optimized for a specific range of magnifications, sometimes fairly narrow, and perform poorly out of range. Systematic testing is the only way to find out for oneself.