I have a new battery tray from RD (purchased a year or two ago). Today I compared it to old battery tray and to the ECU holder and found a significant difference. Here is a pic of the two side by side.
Click to view attachment
And here is a pic of the ECU holder next to the old battery tray.
Click to view attachment
And a pic of the ECU holder next to the new battery tray.
Click to view attachment
The raised area with the hole is missing from the new tray. My car is a 73. Given the condition of the old tray, and the fact that I've owned the car for 33 years, the old tray is probably the original (though I notice that it doesn't have a hole on the front left corner of the tray for the bolt in that location. Is the practice to drill two holes and weld nuts on the ECU holder?