Today I was looking around for more v7 stuff of interest that I might 
find on the web and came across a tape image in the ATT bits directory: 
http://www.bitsavers.org/bits/ATT/ labeled X7252.2015_UNIX_V7.tap and an 
image of the reel with original and added markings. I downloaded it and 
sure enough, it's a bootable v7. I then compared it with my recreated 
tape image from the files in the Keith Bostic folder on tuhs. The 11.7MB 
tapes are nearly identical, with only a handful of bytes that differ at 
the very end of the tape:

ATT tape:
54532000    000000  000000  024000  000000  000000  000000 000077  000000
54532020    052135  014020  010000  034113  056720  023524 072143  122062
54532040    141401  000000  000000  000000  000000  000000 000000  000000
54532060    000000  000000  000000  000000  000000  000000 000000  000000
54532100    000000  000000  000000  000000  000000  000000 000000  037400
54532120    000000 000000
54532123

Bostic recreated tape:
54532000    000000  000000  024000  000000  000000  000000 177777  177777
54532020

I'm wondering - 1) Does anyone know the provenance of the 
X7252.2015_UNIX_V7.tap 2) Do the bytes at the end of the tapes look 
familiar or particularly meaningful? My knowledge of 40+ y.o. tape 
formats is woefully lacking, but I'm curious.

Will