bad motor HELP

my brother took his 92 b2200 to a muffler shop an they told him it didn't have any power because the front cat was stopped up.So they cleaned it out an on the way home it smoked real bad ,when he got home it was almost empty of oil an the tailpipe was coated inside with oil.Even oil was coming out from around the exhaust manifold where it is attached to the head.I went over to his house an stuck a Q tip down the plug holes 1,2an 3 were clean but 4 was full of oil. So now he found another motor an has good compression all cylinders were with in about 10 PSI of each other about 120 lbs.But i saw that number 4 piston has a little bit more movement in it than the rest,will this be a problem?

It shouldn't be, but with any used engine don't exspect to get a whole lotta miles out of it. He should buy the used engine, install it to keep the truck on the road while rebuilding the other engine, then put the rebuilt engine in, then you know what you have, then he could rebuild the other engine for future use, or sell it to recap some money back.

The worst that could happen is some piston slap but it'll probably smoke a little on warm up until the piston swells up, if it still can.