David - I sure wish that manual you linked wasn't missing a couple pages. I thought I had an original copy of it but can't find it now. The missing pages will show Note B which corresponds to the frame extenders, item 19 in the diagram below. I wouldn't have to type the following dissertation if we just had all the pages (but heck, I kinda like long posts
Kraig - you're right. If Willie had a QA latch he could use a rod thru the top holes and it would mount in the QA latch. I've done it below but never really liked it. There is actually another method to mount the blade using the non-QA mule drive assembly. I think it may have been shown on the pages missing from the Manual that David linked. Don't know for certain if that is where I saw it before, but I never liked it anyway since the little non-QA mule drive is somewhat lighter steel and seems like it could possibly twist up.
Willie - the sub-frame you have is Item 15 in the Parts diagram below. It's for a non-QA latch tractor (70/100 and 71,102,122,123 built 1963-67). You are missing the frame extenders (you need 2 of them) shown as Item 19 on the parts diagram below. About 40 years ago I actually purchased a pair of the frame extenders since I didn't know what they were. Can't remember the cost but boy was I surprised when they came in. First, they were painted IH red. 2nd, all they were was flat stock steel (same as the ears on the sub-frame you have) with 3 holes drilled in them. 2 of the holes lined up with the 2 holes in the ears so you can bolt them together. The 3rd hole was where you bolted it to the frame. Wish I could remember how long they were so you could make a couple. All I recall is the space between the top hole (for mounting to the frame) and the middle hole, was a little more than the space between the middle hole and the bottom hole. I'm sure you could figure it out if you want to make these. My WAG would be if there is 1 1/2" between the holes on the ears you currently have, then the top hole and middle hole are probably 2" apart, center to center.
By the way, the sub-frame in the 3 pics that Kraig posted above is Item 22 in the Parts diagram below. Although 22 looks about the same as 15 in the drawings it is NOT. The hanger ears on the front of 22 are alot longer and have 2 pins.