If I get an Alumacraft that has an original straight center thwart, can I replace it with a yoke? I've been trying to contact Alumacraft about it but it's not going well. Do the wood yokes work well for aluminum canoes, are they strong enough seeing that aluminum is heavier than kevlar?
My dad has an Alumicraft from the 70's that has the original aluminum yoke and that works fine for me.

No problem with putting a wood yoke on an aluminum canoe. They are plenty strong enough for the weight. I have a comfy wood yoke on my old Alumicraft Quetico that has been on many many miles of portages.

No problem.

Thanks, any advice for a good yoke, or bad ones to avoid?

Ed's Canoe and Northwest Canoe both stock quality parts.

I just put one in my alumacraft Bought it from rutabaga Just cut it to fit and drilled a couple of holes for bolts works well

How heavy are the wood yokes? Are they heavier than an aluminum yoke or an aluminum thwart?

I didn’t weight them but the straight aluminum was smaller so it was definitely a little lighter. I put superior portage pads on at the same time so it’s noticeable just because of the pads, canoe is the 56# voyergeur would have liked to have kept it there . I should weigh the whole thing and see where it’s at now
(This was a small straight thwart)

17 foot Voyageur is what I'm considering too.

I have done this, replaced with a wood yoke/thwart, on a Marathon / Grumman, so very similar, and have had no problems. Just cut to size and used the original thwart holes.
I would suggest that you use a pipe clamp, or two, to keep the gunnels from spreading before you remove the original thwart.