Front wheel arches and rear corners (rust free imports) from FBI / Ady at Classy Campers / Mark at MCJ imports / Wayne at Volksheaven. Arches seem to vary between 75 and 100 quid each and rear corners between 150 and 250 (not necessarily dependant on condition - seems to depend more on availability at the time.
I got 1 corner from MCJ, one from classy campers and unpicked them and grafted the OG metal back into my van. I got a rust free LHS arch from Evam classic at Dubfreeze and was very lucky to get a RHS NOS arch from Fast Freddy last year.
I wouldn't bother with repro panel unless you have the time / patience to modify to fit (also steel quality these days is not the best versus what was available 36 to 41 years ago!
(Great choice of year and van by the way!)