Re: amc motor mount questions
Add me to the list of folks that have done this switch (in a CJ-7). As everyone else has indicated, the left frame mount is identical for the 258 and 304-360. The right frame mount is slightly different, and carries a different part number. You can check this at the dealer parts department. I bought and used the correct right frame mount (they were available, as of about a year ago). But, after I had the 304 frame mount in my hand, and compared it with the 258 right frame mount, I could see that there was really no reason to buy the 304 frame mount. They are so similar, that the 258 mount could be modified for the 304-360.
As for the block brackets..... the brackets that go between the 304-360 block, and the rubber mount..... I bought an extra set when I was working on my own project. I've only got 20 in them, and they are available to anyone that is interested.
If part of your question is about which rubber parts to use, I believe you should ask for the rubber mounts for the factory-installed 304, from around 1976, to around 1982 (CJ) (unless you choose to use an aftermarket mount, like suggested in these other posts).