Embed Record Form

I have two tables (Table A and Table B) ---- the tables are not related. I would like to embed a specific record from Table B (using the old record form) into a record form within Table A ---

Table B -- I have a number field called [Index]. The index field is unique but it is not the key field. The specific record from Table B I would like to Embed into a Table A form is where the Table B field [Index]=1

I assume I would need a URL formula field in Table A -- that has the "Embed as iframe in forms" checked. I need help with creating a formula that grabs the record from Table B where the [Index] = 1

Any advice is appreciated.