Say I manufacture a receiver and decide to SBR it.

Since I am the maker and intend to make it class 3 I would have to assign it a model and serial number.

So you would engrave the following on the receiver

Maker:
Chase45
Model:xxxx
Serial no 1

Am I tracking this right? Then that info would go into the appropriate "name and address of original maker"

Correct?

Yes, except they don't like the "1" for serial # IIRC.

Or maybe it was model 1 and serial 1 that got them upset.  "But, the Army does that!"  :|

Pretty much, except "original manufacture" would be "form 1 registration" or something like that since it's built from a non-firearm.  That's how mine were done with agent help.

You'll also have to have city/state on the lower, and caliber somewhere on the upper, lower or barrel.

Right on Ill keep that in mind. I just looked at the new form 1s, looks like a bit has changed since I did one last time around.

Any other weird things they don't like in association with serial numbers or model numbers

Does the model number even have to be a real model number? I'm thinking about doing a MP5SD from a flat, but could I put model: Myprettypinkponey

Obviously that's exaggerated of what I would do, but just wondering

Model is whatever you want it to be.  For my .45 PDW, it was my initials followed by "45".  the serial number was the same thing, followed by "-1"

Gotcha

Perhaps its worth a call when I finally do get around to it.

As I understand it, you can make the receiver yourself and register it as an SBR but it needs a serial number
and that serial number should not be something that would be likely to be repeated.

I think if you were to use your initials and create a number to go with it, that'd be OK.

For example, I'd use my initials, digits from the year I made it, and a sequential number for every one I made,
so I'd end up with,  as an example.   A15401B.    AB as the initials, 15 for making it in 2015, and 401 being the
serial number, which I'd start at 400 just to avoid starting at 000.

This is an example, not a real world serial number.  Just something I made up for the purposes of discussion.

Was that the magpul fold down gun you built from airsoft?

Only SN has to be on receiver.

And Model is optional, not required.

https://www.law.cornell.edu/cfr/text/27/479.102

(1) By engraving, casting, stamping (impressing), or otherwise conspicuously placing or causing to be engraved, cast, stamped (impressed) or placed on the frame or receiver thereof an individual serial number. The serial number must be placed in a manner not susceptible of being readily obliterated, altered, or removed, and must not duplicate any serial number placed by you on any other firearm. For firearms manufactured, imported, or made on and after January 30, 2002, the engraving, casting, or stamping (impressing) of the serial number must be to a minimum depth of .003 inch and in a print size no smaller than 1/16 inch; and

(2) By engraving, casting, stamping (impressing), or otherwise conspicuously placing or causing to be engraved, cast, stamped (impressed), or placed on the frame, receiver, or barrel thereof certain additional information. This information must be placed in a manner not susceptible of being readily obliterated, altered or removed. For firearms manufactured, imported, or made on and after January 30, 2002, the engraving, casting, or stamping (impressing) of this information must be to a minimum depth of .003 inch. The additional information includes:

(i) The model, if such designation has been made;

(ii) The caliber or gauge;

(iii) Your name (or recognized abbreviation) and also, when applicable, the name of the foreign manufacturer or maker;

(iv) In the case of a domestically made firearm, the city and State (or recognized abbreviation thereof) where you as the manufacturer maintain your place of business, or where you, as the maker, made the firearm; and

I have only done cans.
I used model numbers as my initials+caliber.
I used serial numbers as my initials+caliber+3-digit serial number.

The oddest thing I ever got back was a sticky-note on the approved form saying I had to use the entire trust name on the can and not the abbreviation I had legally included in the trust formation paperwork.  A sticky-note...really?  How is that vaguely legally binding?  I still use the whole name cause I like it on the outside.  Heck, I would hand-stamp the whole preamble on my cans before I would stop making them.

For my 80% SBR and the 3 form 1 cans I have done I just go with MKI, MKII, MKIII etc for the model and do 00001, 00002, 00003, etc for the serial number and haven't had any problems.

Don't forget City and State.