>What is that weird symbol like a cross, in between 'for' and 'of'?

that's OED's symbol for 'obsolete'; the usage "in truck of" is obsolete: "To.. sell them [negroes] in the West Indyes in trvcke of golde peirels and Esmeraldes." [in trade for]

>Transferatively (!) and figuratively?

transferred sense used figuratively:
"Precedence went in truck, And he was competent whose purse was so." [trading something intangible]

>with a and pl.

the article 'a': "This for That, is rather a Truck than a Benefit."

keep in mind that this 'truck' is not the same as the mode of transportation, which has rather a different etymology.