How not to take something for granted, re accuracy

[tbonesmith]

any suggestions how I correct the forend droop, perhaps with steaming? I've not done that before, how does one set up a steaming rig?

As it turns out I've been doing a bit of steaming timbers of late myself, and what do you know I took some photo's!
So you make a box of the appropriate size for your pieces of wood, make it 5 sided, then you connect a steam source, I used a wall paper remover, which is like a boiler with a hose coming off it.
Put you timber/s in on cleats which just keep the timber off the bottom so they don't get soaked with liquid condensation put a towel over the end and turn it on.
I needed a really tight bend in some 1/2"*1/2" mahogany and it took 3 hours of steaming.

Once your timber is suitably subtle (the longer you leave it the more pliable it becomes), you pull it out, and clamp it to the shape you want it to form, and maybe go a bit further to allow for some springback (a few degrees), then leave it clamped in situ on the jig for a few days to a week and then pull the clamps and it should hold the formed shape pretty well for ever (the springback will be immediate on clamp removal). It may creep a little over time but it shouldn't much if you leave it in the clamps long enough.
Here are the pics!

For what it's worth I would give you odds on, that you would completely ruin any SMLE forend that you steamed in order to bend. I could well be wrong, but I would anticipate unpredictable warping of the timber through the grain, as the section of timber is so uneven ie thick here, thin there, lightening cuts, holes etc grain often at 45^0 through the section.
Good luck though!