We've been here before! This is a 4 sp 3.55 8 3/4" rearend.
I got rid of the anti-freeze the first time for the flush for years of use, the second was to replace the new rad hoses that had wire inside that rusted like crazy in about 1 month. The last one was when I pulled the heads and it ended up with a ton of oil in it, because I can't get the drains out of the block and was afraid to break the bolts!