Which block-poll

[Mr70]

It wouldn't surprise me if someone later on tries to claim that CE engine as the one that replaced the original,6 mos. after back in the day...especially since this is a real COPO we're talking about.
I would go with block #1,but take it a step further and stamp DONOR,with your phone number afterwards into the bare engine pad.That way other owners after you will have a difficult time trying to "massage" it to look like the authentic original,or a later replaced service engine.
Mark the block secretly in another inconspicious area as well,with something only you know,to ID if need be in the future,just in case.
I know a few in your position that have done all these tactics and been very successful at debunking the claims of engine authenticity by newer owners later on down the line.