John has really hit the nail on the head with a FBH. ANY second hand engine should be stripped and completely check over by some one who knows minis.
just a example , I have a moke with 1275 that a bloke wanted me to check over. The engine was completely re-build by a company here in adelaide. The engine has only done 500km since re-build and is stuffed. Compression down 2 cylinders, burning oil, and had a nasty knocking sound. The cylinders still had hone marks and the pistons had bugger all crap on them. PROBLEM who ever re-bored it stuffed up on the size for No 1&4 cylinders only by .010"

NO matter what 2nd hand engine and what you are told be prepared to spend extra money and get it checked over . It's cheaper than stuffing up a eng/box

Given the motor we are talking about has done 7,000k's, I would try it (each to their own). There are instances of motors not being built properly, no argument there. But would you pull a 7,000km motor out of a car and strip it because someone you didn't know might have built it and got something wrong - No.

tis a smart man who learns from the mistakes of others, not from his own expensive mistakes

Yes I would because I am not sure that this has travelled 7,000k's, Without Problems

Yes I would because I am not sure that this has travelled 7,000k's, Without Problems and I have seen many a destroyed Crankshaft And Block Just from a simple little Mistake like centre crank thrusts fitted back to front, So I Think a little time spent before fitting Could save Many Dollars But as You say ( each to their own )

You also have to ask the question as to why it had only done 7000km before being removed from the car and then not being reused for 2 years.

Maybe the owner had more than one good motor, like I do.
My 1360 ain't broke and has only done 11,000 miles, but the 1412 stroker is replacing it for a while, next week. Why? I'm just sick of looking at it on the floor!