1) A pistol caliber carbine that is a repeater. Not semi-auto.
Useful for target shooting, the trapline, possibly powerful enough for wildlife protection, cheaper to shoot and less recoil than a full power rifle, and packable for bush camping/boating.
Example: 357/38, 44mag/special, or even maybe 10mm/40sw.
16” barrel, bolt action, short light and handy. Borrow readily available magazines, bases, and make it retrofit to an available inexpensive synthetic stock that fits popular models of preexisting firearms (i.e. 20 gauge 870).
2) Something similar in 30-30 would also be very useful if it is possible to bring the price point down enough below the cost of a Henry. Could double as a smaller persons deer rifle.
3) A similar concept but using as much available M4-type parts as possible. Even better would be if it enabled barrel swapping to have a small bolt action with a 223 bolt head where you could swap easily between 223 based cartridges. Could double as a varmint/coyote rifle. Inexpensive and low recoil as well.
4) Stainless steel dowels for pillar & glass bedding the stock bolt area on lever action rifles like the 336, 1894, 1895, etc.
5) Scope rails for the Sako A7.
I have more ideas but I’ve probably already written too much.