Older flat backs are a piece of cake with a little knowledge and easily my favorite project rifles.
I have one in particular, an 116FLCSAK (was the maxed out deer rifle when I bought it in 96 before being discontinued as a factory offering) in 30-06 that is stunningly accurate and has put a best 10 shot group into .446 with Sierra Game Kings and IMR 4350. It always turns heads at the range. It shoots the lights out just like it came out of the box except I lightened the trigger a little.
Plenty of easy, economical do it yourself upgrades to be made to the old flatbacks if you like projects including tuning up the 3 screw triggers ( a crisp 2# is easy), bedding the stock (epoxy from the hardware store), adding a bolt lift kit ( a piece of .38spcl brass and a small ball bearing), are a couple that immediately come to mind.
The accustocks are an improvement over the old "tupperware" stocks as far as rigidity but the older "tupperware" stocks are quite serviceable. The only "flex" (which seemed to be the biggest complaint about the older factory synthetics) that I have ever noticed was on a heavy long barreled 110FP when using a bi pod on the front stud. In my opinion that particular stock due to the heft of that rifle was just a little bit too small of a barrel channel and not quite enough stiffness to support all that weight.
I actually like the older "dual pillar bedded" factory stocks for shorter barreled rigs and sporter barreled rigs because of their light weight, durability and and their weather resistance. They are also pretty easy to improve in functionality and appearance.
Good luck.