I'd think they are very probably mutts.
First one, some american companies made their own no5s, sometimes called "tank carbines", not genuine. Some ppl privately shortened a no4 barrel and made a gun using no5 parts, a bush gun, not un-common here in NZ. A real no5 Ive only ever heard of as British
made, so a No5 mk1 and not a no5 mk1*.
Second one, if its an Ishapore I'd think it was a no1 mk3* receiver and not off a no4 receiver so I have no idea what you have got. Some of the american companies put 7.62mm barrels on their "tank carbines" as well I think.
So, if you upload some pics that would be most helpful.