To echo the comments above, great trip Rian and thanks for taking us along
Regarding the blazer, I had a ‘78 many years ago ( well GMC high Sierra ) it was actually very reasonable on gas would do low 20’s. Also for me other big ticks in the plus column; it will qualify for classic insurance so mega cheap and also FREE road tax next year.
Other options for improved mpg would be an lpg kit or even better swap the motor for an oil burner. A mate put a diesel motor and auto box out of a bmw 5 series in his C10 truck, with it being a I6 and 2 wheel drive in dropped in no hassle and was like 40 mpg and still went well. He also sold his 350/TH350 combo for more than the diesel motor cost him :
Go on you know it makes sense