Bigfan,
I've been working on my own newly acquired and my first MV myself. It can become challenging and a PITA at times, but I love it, it keeps me on my toes.
With that said, keep your head up, and as they say, "hope for the best but prepare for the worst". There will be good times and there will be bad times. Ask questions, and as I have found, most of the members on here are GREAT and are a wealth of valuable information and will help you out, a few not so much!
As I was told early on when I received my MV, read through the TM's and learn the truck. The military TM's are different from the civilian vehicle manufactures factory service manuals, and it was a big learning curve for me. The only problem I have found with the current TM's are that they are for the A0's and not directly for the A1 or later. I have found that most all of the information in the current TM's relate directly to the A1's, but are missing some information for the A1's, as I have found.
The TM's are on this site but I downloaded the current TM's from this site. I believe these are the most current TM's available. Someone please correct me if I'm wrong.
NSN Center - Advanced NSN Database with NSN Search
www.nsncenter.com
The first 10 and the last 3 TM's are for the M1078. Just click on each one you want, when it comes up, click on the red rectangle with "pdf" in it and it will load up the TM and you can save the file.
In reference to the high speed gears, I had looked into them also. Wow, crazy prices, hope you have deep pockets. You only need two, I need three for my MV. Crazy money!!!
As for the drive shafts, they are out there and I have found several member sell parts on here. Two of the three axles on my MV were damaged and had flat spots on them. It appears someone lifted the truck up with a large fork lift and damaged the front drive shaft and the drive shaft from the transmission to the intermediate axle. I removed them and took them to a business that build and repair drive shafts to have them repaired. One of the two damage shafts had to be completely rebuilt the other half rebuilt, and all three were balanced.
The drive shaft guy said that none of the three shafts were ever balanced. He said that he knew this because none of them had weights on them. He told me that no matter what, all drive shafts, new or used need to be balanced and if they have no weights on them they were never balanced. He also told me that most of his time is spent on balancing shafts from brand new trucks because they were never balanced to begin with. So, my point is when you get new shafts have them looked over by a experienced professional and have them balanced.
As far as any secondary damage from the drive shafts, the above comments from the
more experienced and knowledgeable members are correct, look for additional damage to other parts.
Good luck, have fun with your MV and hang in there!
Be safe.