I don't think anything on the 38 will fit the 99.
That being said, First make sure Bubba knew what he was puting a stock under. the early Arasaka was a great and strong action. The late or last ditch guns are unsafe to fire.
I have a type 38 that was rebarreled by E.R. Shaw in Bridgeville Pa., Just outside of Pittsburgh. The type 38 is short action so I had it barreled in 260 Rem. They did a great job. The gun will clover leaf at 100 yrds. and has droped deer in their tracks at over 200 yrds. Shaw finished the barreled action in flat black and it looks great on the birds eye maple manlicher stock. It is a fun gun and many people have no idea what kind of gun it is and are really suprised when they hear it is an old Jap. The gun is a good conversation piece around the camp.
All that being said, The Type 99 is a long action. I am a 6.5 fan. The 6.5 doesn't kick and will kill a deer at a longer range than most people are willing to or capable of shooting.
My opinion.........E.R.Shaw 6.5X55 Sweede. Timney also makes a good side safety trigger for that Jap. too. I use one on my Type 38.
Oh.... since you already have a nice stock, My Shaw barrel was a little wider that the 6.5 military barrel and only took a little sanding to make it fit. The Shaw did not have the military contour but was wide enough that materal needed removed from the stock.