I made the lip with a plactic spoon. Imma use it on a bait caster for silver salmon and king salmon.
IF you used a basic plastic spoon like you get at a fast food store, it won't hold up. The plastic is too thin & too brittle. I like that you're thinking and trying to use what you have, but first rock you hit with it, it's probably destroyed. Most likely too if you don't break the lip casting or retrieving and do hook up to a Salmon, it's going to get broken and will be a one fish lure. Places like Lurepartsonline that Capt Bob suggested will have plastic lips that are more appropriate for what you intend. There are other good sources too for lure components.
I know a lot of folks who make lures and there is a debate about thru wire and screw eyes. I've fished lures that were made both ways and have caught plenty of fish. But, it will depend on the fish, how big & how strong they may be & how well you build the lure which method is more appropriate. Soft woods & screw eyes may not always work well together.
I lost a rear hook on a wooden lure once, because the builder skimped and used screw eyes that were too short. The whole screw stripped out of the wood. This was done fortunately on a snag and not a big fish. Since then, on lures I've bought that had screw eyes i would take them apart & check, and epoxy them back in place, and replace the screw eye with longer if I thought it was needed. I've never had that happen with thru wired lures, but have had a few get wet & swell. That meant the wood was not properly sealed. The guys who build wood surf lures and know what they're doing all have solved these problems, which is why folks buy their lures and pay the price they charge! Building these wood lures is not particularly difficult, but there are "details" that you would be well advised to learn about if you're serious about making them.
Just for your reference, I'm a big fan of RM Tackle, who makes surf fishing, wooden lures. Check out their website (https://www.rmtackle.com/) and look at the detail of the lures there. I know surf lures & lures typically used for Salmon are not the same, but there's a lot of similarities in building any lures from wood. You might even get some cool ideas from the visit!
I also know a fellow in Japan who has some seriously mad skills when it comes to making lures. If you have an Instagram account, check him out. makilure2018 His talents are way out there and I think you'll enjoy looking at what he makes!