The MH/CH-53 is definitely on my list at some point, definitely an awesome machine! It was never used by the Army, but the Marines, Air Force, and Navy have used variants of them extensively. I would love to do on as either USAF Special Ops:
Or a Vietnam era Super Jolley Green Giant
The issue with a CH-53 is that you have to go big to get the true presence of one right, and every step bigger in Helis seems to about double the price tag. I have a 700 size on the bench, and it's taken over a year to slowly purchase the parts and electronics, and I'm still not done. And the CH-53 uses a 6 blade rotorhead, which would have to be custom machined.
However, I do have those 700 size mechanics set aside for one project. I would like to build a Bell 525, which is the helicopter that I work on. This will be a totally scratchbuilt fuselage, so the timeline may run a bit long, but I'll post a thread whenever progress is made.