As noted above by Eagle 27 I have built my 404 on a FN Colombuan 98 and it feeds as slick as could could want. I was fortunate in that my GS understood the requirements for good feeding symetry and we used the standard ex mil box and follower along with the bottom metal that was changed to button release in the floor plate. Did have to re-look at the retention of cartridges as Eagle 27 noted but that was because the 350gn GC bullet I designed had a bore riding nose that was wider than the usual Woodleigh that we had origionally set up for. All it took was to take the milling of the mag box side walls further forward ( it had only gone forward enough to suit the Woodleigh nose shape)to allow the cartridge to lay more to the outer side of the box. It retains and feeds ALL cartidges under any enthusiastic working of the bolt now. It comfortable holds one up and three down.
Good to see you are going to have the two rifles that will handle ALL of you big game needs.

If you PM me your email I can send you a write-up I did on the build as it is probably a bit long to post here.

Von Gruff.