I have a new MDS .58 on a CAP 232. MDS recommends a 11x7 for break in. Is it
OK to use a 11x6 instead? Also, any thing I should do to this engine before or
during break in?

You should be fine with the 11x6.

For break in, you need to know if the engine is ringed or ABC/ABN. Then do a search on this forum for break in procedures, there has been a ton of great stuff written here on how to do it for both ringed and ABC engines.

cj,
I'll paste some info on ABC engine break-in from another reply I gave. If your's isn't ABC or ABN, ignore it and find proper procedures.
Dennis-

ABC engines have an Aluminum piston in a Chrome plated Bronze sleeve (ABC), or Aluminum piston in a Nickel plated Bronze sleeve (ABN) which the OS's actually are.

Because of the different rates of expansion of the piston and sleeve, the sleeve is bored to a taper making the piston/sleeve fit "squeekey" tight at top dead center. (Sometimes they're so tight it's difficult to turn them over when cold.)

IF you run one of these "4 cycle" rich, the excess oil/fuel will not allow the engine to get to operating temperature, and the piston will rub against the sleeve causing excessive wear. The end result will be too little compression for a good, powerful engine.

Proper break in? Tune the engine until it's completely 2 cycling (at full throttle obviously) but not peaked, and run it for 3 to 4 minutes. Shut it down and allow it to cool enough to touch the cylinder head.

Restart the engine and repeat. Run through at least 2 to 3 tanks this way, then you can fly it. Do not lean the engine much beyond the break in setting until you've run a couple more tanks through it.

Of course, you never run an engine at "peak" RPM, always at least 300 - 400 below peak. (They lean more in the air when the prop unloads.)

The smaller propeller is fine. Just remember, you do not have to fly at full throttle all the time. The left stick does work! (Mode 2)

Well, I have to say that this new MDS is one tight puppy. I now have six, yes 6 stiches in my finger to prove it. But, I didn't let that stop me, I managed to fire it up and am in the break in process. Thanks.

That makes it sound like you cut your finger on the prop while pushing against compression, not from a backfire?

First, you should use a chicken stick or something besides your finger to avoid that kind of problem. (I guess you figured that part out on your own though).

Second, depending on the prop, I usually shave or sand off the mold flashing on the prop to make it more smooth and less likely to cut my fingers when doing simple things like priming and such.

OK, yes it was from the compression. What do you mean by the mold flashing.

Sand the edges of the prop to remove the flashing and make the prop blades less sharp. I cut my finger once taking a Master airscrew out of its plastic package.