The 406 will like more cylinder head than a 350. Have you thought about using the AFR 210 or the Edelbrock Victor Jr. heads? I have Performer RPM heads on my 406 and will step up to the Victor Jr. on the next engine. Check the mid lift flow for cylinder heads in the 210 to 220 intake volume range and you will see that the Victor Jr. heads have a lot to offer while still keeping a great price.
AFR sells a lot of cylinder heads and it would not surprise me to find that they were on back order. I would not call a 5 week wait normal, just a fact of supply vs. demand.
The best place to purchase may be the store that has them in stock if you want them right away. The reason that they have them in stock may be because they do not offer the best pricing. How soon do you want to go fast?
How many RPM's you get out of an engine is as much a factor of camshaft as cylinder head. Both the cam and the heads have to be operating at their best in the same RPM range to get best performance from the engine. Try to not put too much stock in the stated RPM ranges listed by the manufacturer's as they are using a 350 as a baseline. The 406 is nothing like a 350 in reguards to these suggestions.
Good luck with your project.