The first step in the conversion of the Parkside kit is to insert a scale 18in into the sides and floor. The most convenient way to do this is by inserting two pieces of 3/16 x 0.060in Evergreen strip into the body sides either side of the door. Purists will note that 3/16in equates to only 4.8mm; slightly short of the 5.25mm required. However, as the next size of strip is 1/4in (or 6.35mm) the error, which scales to l.5in, is tolerable in return for the convenience of having strip which is truly square edged. There are minor differences in the ironwork between the GNR and LNER versions in that the joggle in the body knees (the heavy forged bars that support the body sides either side of the door) goes through the top of the curb rail instead of below it and, because of this, the diagonal braces are attached to the bottom planking bolt instead of the curb rail bolt. Altering this requires that the foot of the moulded body knee is cut back and the diagonal braces removed to be replaced later by a strip of Evergreen plastic. The door also needs the plates for the door stops removing, as the GN version used a single stop bearing on the central strap. Strictly speaking, the angled bottom plank on the door is wrong for a GNR wagon, but removing it would be tricky and, given their almost universal adoption later, there is every probability that the door could have been modified later in life. The ends require modification by the substitution of timber end posts, made from Evergreen 0.080 x 0.080in strip, for the T-section steel bars used by the LNER. With this done, the body can be assembled in the normal manner; the floor is lengthened by the addition of two pieces of 3/16 in strip.

Unlike the LNER version portrayed by the kit, the great majority of the GNR wagons had a wheelbase of 10ft Oin; the remainder were variously 9ft 6in and 10ft 6in. Thus the solebars need to be lengthened both at the centre and at each end. For the centre section, rather than simply let in a 7mm section of strip, I cut the sole bars behind where the centre door stop would go and behind the left hand body knee, as that would later allow the joints to be hidden. The ends were extended by the addition of a piece of 0.060in strip glued onto the end of the solebar; again where it will later be hidden by the angle brackets used to attach the headstocks to the underframe. The RCH pattern axleboxes provided for the LNER wagon are inappropriate for the GN version, which used the GN / LNE standard open fronted axle box. I had some cast LNER axle boxes and W-irons spare from another kit.

An alternative, had I had them to hand, would have been the BR pattern open fronted axle boxes that come as extras in some Slater's kits, as would have been using the complete underframe mouldings from the later Parkside kit for the LNER 12 ton van (PS45).