The Forums will be down, Friday, November 24th starting 8 AM PST for upgrade.We'll probably be down until 1PM PST, but it might be longer. I'm doing a major forum software upgrade, so I expect the forums to operate somewhat differently when we come back online.
I usually build 1/24 - 1/25 scale but I currently have several 1/32 scale cars started & maybe 20 or so more 1/32 kits.(maybe 200 1/25 scale} I may get around to building some of them, but like a lot of us I have more unbuilt kits than I have life left. I probably have at least 3 of each scale started. I'm trying to complete some of those before starting others, I will concentrate mostly on 1/25 in the future. I have a growing collection of 1/64 die-casts & some 1/25 die-casts. I also have 2 1:1 collector cars to contend with. I hear HO scale calling too!
If it is the wood grain on the plastic that is causing the contrast concern, perhaps you could sand the wood grain on the plastic to lessen or eliminate the texture & then do your wood graining technique as it looks very realistic. When I saw your practice piece I thought you had done it on balsa wood, Also, keep in mind that there would be some contrast in the grains as the framing wood is a different type of wood than the panels. Also if the wood has a new coat of vanish, that would have an effect on the appearance of the grain. You have probably taken all this into consideration, but I know sometimes I tend forget about the forest when looking at a tree. (just trying to maintain the same "timber" with that last remark )
I had the kit when it was current but lost it & 99% of my models in a move in the '70's. I bought one a few years back on Ebay as I have become a fan of the slant 6. It was a complete kit but has a tire burn on the windshield.