Ive done several Iguana mounts they have worked very well for me with some work.
the tricky spots for me where the head tail and toes as mentioned.
the tail and toes go slow and be carefull thats really your only option. on one iguana i did a cast tail in resin for the last 5 inches tricky but it worked.
for the head you have a few options
but before you do anything to it make an alginate or silicone mold of the head. iguanas have a great deal of personality in thier faces. the iguanas i did where for pet owners and they new thier lizard!
so your options
1. skin the head. go slow and easy use a sharp xacto knife and move slow!!. you can then put the skin over either a carcass cast of the head or make a second cast of the head before skinning and grind it down.
2. use an artificial head. this is the option i liked best. it looks a thousand times better in my view, but I am a sculptor by trade so i enjoy this bit.
the way i use an artificial head is, I use a casting off of the iguana. and grind down everything below the upper lip just below the lip line. so actually only the upper part of the head is a cast, it works well the exspression is there and I am able to set the eyes ahead of time. the skin is still used for the lower jaw and lip.
this is all very hard to explain sorry. I have included a picture

the bright purple is the visible cast head. the dull purple is where i have ground down the cast to accept the skin. at this point i even use apoxie to sculpt in the areas around the dewlap.
mother nature has provided you with a nice seperating line where the cast and skin will meet.
I hope this made sense at some point I would like to do another iguana and document the whole process step by step.
If anyone knows where to get ahold of an iguana feel free to send me a message, like i said i only did pet owners animals. but thier population has increased in the last few years in florida.