I think the answer to your question depends on just what engine you are swapping in and what else you have done with the rig. If you have kept the rest of the rig completely stock and then you drop in the Chevy engine yes it will hurt your resale value because the folks who want a stock, original rig will run away from the Chevy transplant.
On the other hand if you have done mostly Toyota based upgrades to the rig so it isn't stock but it is still all Toyota, you will probably get a similar reaction by adding in the Chevy small block.
Obviously if you mod the rig using whatever you feel like so while not a hard core truggy but not at all stock then the Chevy block should be a plus up in that market.
I'm a second paragraph kinda guy. Swapping in a 1HZ, 6 cyl 4.2l Toyota diesel to replace the original 4 cyl, 2.9l Toyota diesel. I have done mostly Toyota upgrades and in my case the swap is a plus up. The key here is don't worry about re-sale value, you will never recoup your investment in the rig. Swap in what will work for your needs and enjoy it>