Yes you missed something. He asked for a 3 shot mag with longer than factory dimensions. You showed him a factory remington cdl dm, which will not be long enough. He uses a wyatt box to get the extra length. The mag you offered is a standard remmy part, so i imagine will not be difficult to obtain, either new or s/h.
Its odd that you choose a single shot action in a chassis, odd to me anyway, i’d have had a nice stock on a single shot rifle or a repeater in a chassis.
looks nice though