The four "tu56" files here come from four DECtapes read at the LCM+L.
They contain a port of 6th Edition Unix done by Tom Lyon and others
to IBM's System/370. An email from Stephen Jones says:

    Tom Lyon says that they were written using 'tp' on v6 unix pdp-1145.
    No errors on the reads :)

Warren Toomey used the 'tp' utility to extract the contents and create
more modern tar.gz archives of the tape images.

Tom has written a series of articles about this port of Unix on his blog;
the links are:

 + https://akapugs.blog/2018/05/12/370unixpart1/
 + https://akapugs.blog/2018/05/12/370unixpart2/
 + https://akapugs.blog/2018/05/12/370unixpart3/

Local copies of these blog articles are copied here.
 NameMtimeSizeType
0 370_c_virgin_source.tar.gz 2019-08-01 21:57:47Z 63 KiB application/gzip
1 370_c_virgin_source.tu56 2019-07-31 00:43:02Z 290 KiB application/octet-stream
2 370_unix.tar.gz 2019-08-01 21:59:45Z 101 KiB application/gzip
3 370_unix.tu56 2019-07-31 00:43:06Z 290 KiB application/octet-stream
4 README 2019-11-04 23:28:16Z 709 B text/plain; charset=utf-8
5 Tp-progs/ 2019-08-01 22:05:03Z 16 B dir
6 image1.jpeg 2019-08-01 21:44:12Z 648 KiB image/jpeg
7 image2.jpeg 2019-08-01 21:44:14Z 623 KiB image/jpeg
8 modified_370_c_compiler.tar.gz 2019-08-01 21:56:38Z 97 KiB application/gzip
9 modified_370_c_compiler.tu56 2019-07-31 00:43:11Z 290 KiB application/octet-stream
10 toms_blog_pt1.html 2019-11-04 23:29:15Z 716 KiB text/html
11 toms_blog_pt2.html 2019-11-04 23:29:16Z 412 KiB text/html
12 toms_blog_pt3.html 2019-11-04 23:29:18Z 743 KiB text/html
13 unix370_c370_assembler.tar.gz 2019-08-01 21:58:57Z 34 KiB application/gzip
14 unix370_c370_assembler.tu56 2019-07-31 00:43:15Z 290 KiB application/octet-stream