Looking at a ‘76 how easy to add OD?

[Fishwater2002]

Are you saying that the transmission and transfer case have been changed ?
A Blazer/JIMMY in 1976 with a 400 engine would have only come with a TH350/203 combo - TH400/203 first year was 1977 and only in 3/4 & 1-Ton trucks and the TH400/205 setup wasn’t offered until 1980 ( and only in 3/4 & 1-Ton trucks ).

Since your JIMMY doesn’t specify a gear ratio code on that SPID that indicates that it has the standard gear ratio which is a 3.07 ( see pic of standard ratios ).

Adding an O/D to a 3.07 geared truck might put the RPM’s a little low and hurt the driving experience.

Take some good pictures of your trans & T-case and we can identify what you actually have and possibly explain the easiest route to a trans swap.

View attachment 533657

Serves me right, I googled it and the 1M40 came up as a T400 but I just saw the pics from the inspection and it’s definitely a T350 pan. The truck is getting shipped to me so I’m having to go off of google searches. I also didn’t see 3.07 listed for the standard ratio so that’s probably a pretty good gear with 33’s for highway cruising, I’ll be taking it to camp every weekend and it’s about 50 miles each way in two lane highway which as I mentioned above was not enjoyable with 3.23’s and 26” diameter tires…

 

[HankScorpio]

You need to forget about car ratios, 3.07 is the first thing to change. 33's on a carb V8 is going to feel very underpowered if that is the true ratio.

 

[HankScorpio]

Gear Ratio Calculator

Good gear calculator here