1970-76 spare tire tub differences

[Broman]

Regarding the deep (full-size) spare tire tubs, I have seen two differences.

1) Some have one drain hole (fwd) and some have 2 (fwd and aft).

2) Some have what looks like a heat shielded welded to the side next to muffler.

The question: what is the date of these changes?  Before I weld in my salvaged tire tub I wanna make sure I have the correct one.

[Paulytunes]

This is mine (build date of 7/76):

One forward plug and one aft plug.

[Monztr]

What year is yours? 

[Broman]

On 1/10/2025 at 2:06 PM, Monztr said:

What year is yours? 

May 1971.

I dug around and found the original, old rusted-out one from may car...one drain hole.  So sometime between 5/71 and 7/76 they added a second drain hole.

Also, my 5/71 tub did NOT have a heat-shield on the side.

Here's a pic of a later tub that has the second (rear) drain hole and a heat shield.  I wonder when this change was made.

[dutchzcarguy]

Someone with a microfiche system can find out the dates.. (I do have the microfiches but not a functioning viewer.. unfortunately)