You seem to be a person that keeps your lift for a very long time. Allis-Chalmers Material Handling went out of business in 1986, the reemerged as ACMH for a few year and were bought out by Kalmar, Sweden and operated as Kalmar AC and Kalmar AC was around until about 1999/2000 when Komatsu bought them out. Komatsu provided trucks to to Kalmar AC with only a paint job & decal difference and were sold through a different dealer organization. The Kalmar AC dealer organization (or Tusk) no longer existed as of about 2005. All that means is that keeping eithre of these truck you have up adn running migth prove to be a challenge in the future. I suggest you strongly consider buying a the new truck from the dealer that you are currently using to keep your existing truck up & running. They know you and your equipment. Others may not be as resourceful.
Do all the things others have already suggested
But remember a few things 1.)Being big is not always mean better. I worked for two big dealers and their main focus was on large accounts vs the 1-2 truck users - main reason it easier to help pay the bigger fixed operating cost associated with being big. 2.) Being #1 in the business only means the next position one can move to is less than #1 - ask Sears Roebuck & Company, General Motors, etc. etc.
3.) Some dealers will represent more than one product line of the same type products - in a couple case two companies builds two brands at the same production facility with the only differences are paint, decals and marketing policies and very little technical differences, if any. I can think of two. When a dealer represent several brands of truck from different manufactures - do your best to find out what dealers resources are dedicate to the brand you are considering - by resources I mean service parts on the shelve and lead time if not (sometimes 90+ days to get a part from overseas is not good) technically trained (certified)technicians on the product you are looking at, rental units available if a unique type truck etc.