ok guys thanks for the input let me try to make iot a little clearer
i am in england gas is $10 a gallon!
lpg (propane) is about £4/5
diesel is about the same as petrol ($10)
truck is a 49 stepside to use everyday
so i need either a good torquey petrol (hopefully a v8)
wich with the right combination of rear end/tyres/right foot/transmission will do maybe 20 mpg??? a cam and headers may help this i can then run lpg through an impco 425 propane carb
and as lpg is half the cost of petrol should then equate to 40 mpg wich is fine

OR
i need a lazy reliable diesel wich will do maybe 30/40 mpg BUT i then wouldnt have the ,,noise,, and the fun of the v8 when i wanted it + i would have the stinking rattling noise ,,but,, they are super reliable and very very torquey

another option i thought was a english gm straight 6 these are bulletproof in a car these do 20 -30 mpg have a bit over 200hp are very cheap but theers the electronics issue no big deal but stil another job
+ car mpg is not truck mpg

at the mo i ,,think,, its a 216 but with gmc on valve cover i would imagine this is just thirsty and slow but torquey?

whaddya think guys?