I noticed a lot of interest and since I just did it, thought I should share.
I bought a Sharp convection from Lowes. It has to be a zero clearance opening door to fit. Sharp only makes 2 with these doors. I like Sharp so didn't search for other brands.
There is a screw in the top cabinet under the plastic cover next to the existing unit that needs removed then remove the others after you pull the trim off the front.
I couldn't use the old mtg. plate so installed new one. There are 2 screws that go thru the top and into the new oven from the cabinet above the oven. You have to drill holes in the bottom of the cabinet to access these mounts . I measured carefully and had to still elongate both them. There are 2 long screws that go into the back plate. I had my son help me lift the new oven into place and held it with a bottle jack while I secured it. The electric cord head also needs a new hole in the cabinet as it is in a new location as well. It's a fairly big job
I replaced my original convection/microwave with a Sharp microwave and went through an identical procedure. It wasn't easy but with the help of a friend we got 'er done. If I was into cooking with a convection oven I would have tried to find a direct replacement but since I only used it as a microwave I saved the hassle and the $$$.
Dans9, nice job. While a big job, it is one we can do ourselves.
Here is our Microwave replacement info:
Replacing R-1830B Microwave with R1875-T (http://beamalarm.com/Documents/replacing_r1830b_microwave_with_r1875t.html)