I have only seen a handful of these over the years, so I'd say its valuable (how valuable, thats up to you)... Much better looking then that HUGE gas gauge!
Back when I was in High School (okay, so I am bored today

), I drove a
'78 Blazer 4WD... My mother (a Hot Rodder at heart) purchased it; headers, 4" lift, 33" tires... After a few months, she realized it was difficult to get my grandmother into it, so she traded me for her Ford Station wagon she let me drive (Thank God!)...
That thing was FUN!... a previous owner put manual hubs, and I discovered that if I put it in 4-wheel-Low it was really only rear wheel drive. Top speed in 4WL was only about 45, but it was a rocket up to that speed!!!

And the stock tranny would chirp the 33" tires...
Unfortunately, I driopped the driveshaft pretty quickly (with 3-week old U-joints)... Mom wasn't happy...
Finally, mom's mechanic (I was still learning) told her is was missing ALL the smog equipment (its great being in California), so she sold it (offered it to me first, but the smog worried me (needed tires too, etc)...
I ran into a subsequent owner, and he was so happy... Turned out in was a factory HD (8500 pound GVW ?) version, very rare for a Blazer... It
wasn't "missing"
any smog equipment, it was EXEMPT!!! No AIR pump, no Catylitic Convertor, it still took "regular" gas (no restrictor in the filler neck, not "unleaded" on the gas gauge...
factory 400 small block, 3.73 gears, and that tach...
I was just thinking about it the other day... Wish I took it when offered...