Ruby managed chicken necks, and frames really well when she was little, I even gave legs too - they just took a little longer to get through (was soo cute watching her work hard for it- they're gone in two bites now lol). Just a tip, when Ruby got bigger she started to just swallow the necks whole so I stopped feeding them after that. At first I also ground the offal up and mixed it with her ground meat so she wouldn't turn her nose up at it - she was kibble fed when we got her so she wasn't used to offal. When I knew she was used to it I just started giving her chunks. But it sounds like your guy may already be raw fed so he should be used to offal and you wont need to trick him like I had to lol. I know you really, really hate fish but some fresh sardines or other small type of fish will be managable for puppy too. I have also heard of Raw feeders who will give the pup bigger RMB's, let them do their best with them (they say it's good practice and it keeps puppy busy - which keeps them out of trouble ha ha) and whatever is left they remove and feed it to their older dog(s) in their next meal, just make sure pup is still getting adequate bone from elsewhere until he can actually get through the bigger RMB. Last tip as you will be feeding two dogs raw now you may want to invest in a freezer so you can buy bulk to help save money lol (do you still have the link that Eli gave you of her supplier?) I feed 30kg a month so eventually you will be feeding around 60kg per month - thats alot of meat!
Welcome to the Hub Paul

your dogs are gorgeous