I agree with do the cradle mod and move on. Out 1st Quietline was my Twin-stick 1450. After I bought it, I noticed the muffler box was touching the left side panel. I loaded it up, took it to Dads and we tore it down. The PO hadn't taken care of it properly, it had the "normal trilogy" happen. The some of the pan bolts went loose, then missing, which got to working on the rails/rubbers, that finally "machined" some of the oil pan off.
Just to be safe (remember this was our 1st Quietline) I found a good set of used rails. Started some research on here and found the cradle mod. I also purchased a cast iron pan, new ISO Rubbers from Charlie and a few other goodies. This tractor was down for a while because of other things in life at that time. So it was several months, from start to finish, but I had another tractor to use. We replaced the pan, did the cradle mod, put on new ISO Rubbers, a rear lift, pinched the front axle channel and replaced the pin with a bolt, put 1 inch spindles off a parts 782. It's been one of my primary tractors since, and I haven't had to do anything with the ISO Mounts. I do however, on a regular basis, check and make sure the pan bolts and ISO Bolts are still there and tight. I've never had to tighten them, as they have stayed put.
We now have 5 Quietlines, and with what we learned on my 1450, the first thing that happened when we got them home. We pull the engine, order new ISO Rubbers, drop a modified cradle in(remember the extra set of rails, we keep a modified cradle on hand most of the time), pinch the channel and put in a bolt. If takes a few hours, and then we don't have to worry about them again. We make a habit of checking the engine mounting bolts on all our Cubs, including the solid mounted ones, just in case (I've seen ones on those loose also).
For accessing the pan bolts, I use a GearRatchet. It's one of those the fastener will pass all the way through and they are shorter than a normal socket and ratchet.
As for the decision to use the rails and ISO Rubbers, was to address the removal of the balance gears. The balance gears did their job well, as long as they stayed inside the block. Remove the balance gears, and the 14's and 16's vibrate horribly. So to counteract this vibration, they had to do something, so they went with the Rails and ISO Mounts (not the same execution, but same idea Harley-Davidson used). The weak link in the design was the 2 independent rails (which they addressed in later series, as mentioned above). Make the cradle a unit with the mod and it works great. In my opinion, solid mounting a 14 or 16 single with no vibration mitigation is not an option. They need the balance gears, or rubber mounted, or a solution like Dave Kirk has with the crank weight modification. We have a 149 (My favorite tractor of all the ones we own) that on the last rebuild, we removed the balance gears, due to the wear in al the components, and the recommendation of many on here. With the vibration introduced into the frame and running boards, after less that 30 minutes of running the tractor, Dad or My legs start to go numb. We used to run this tractor for hours on end.... now we only use it when needed. Now we used one of the Quietlines, or the 782 (twins don't vibrate like the singles do) for all our work. I still like running the 149, but I won't run it all day if I don't have to......
Here is the ratchet type I'm talking about: