Front seat mounting brackets

How big of a difference  is there between the front seat mounting brackets, if the p/u matters, in the INNER BRACKETS AT THE DOGHOUSE, between the years of 1961-1964 and 1965-1967?
Is the seat bracket length wider in the 1967?
Does the 1967 seat bracket sit higher?
Is the welded on brackets that mount the seats to the bracket any different?
Is the mounting to floor board holes different?
We've modified the doghouse sides to accept a V8 so I am needing the best way ( I know I will still need welding and modifications to these inside brackets) but if the 1967 give me a better head start at this, I will attempt to purchase the 1967 inner brackets. (If this way is  worth the difference).
Or should I just modify the brackets that I already have (the 1961-1964 inner and outer seat mounting brackets?
I am using Fiero seats.
Any info will help.
Thanks,
Dennis wagner
561 267 8493 no text
or 561 2369206 to text

https://vintage-vans.forumotion.com/t54501-smittybilt-44801-black-low-back-seat


I dont have all the history for what changed over the years but for my 62 I found some distinct differences between the driver and passenger side inner brackets.  

Brackets on drivers side were shorter due to how they attached to the for/aft adjuster.

There was a response at the end saying there were some changes but it didn't seem to match what I found and pretty sure mine are original but seems similar to your description.

Ultimately I just removed the adjuster, raised the drivers seat bracket and made different adapter plates.

You must have a mixed set of brackets,i.e. 61-64 style and 65-67 style as both should bolt up to same width. Early ones had the wider pattern thru the tubes, late were narrower thru the inboard tabs welded to the tubes.

Thanks for your reply.
Great job on your seat installation.
Tim from USA explained it on your seat installation, which I hadn't seen his reply before.
Thanks,
Dennis