Gary-
No problem installing a '36 tank in a '35. That is what I have in my '35. However, the neck curvature is different. You must use a '35 neck for a '35. As far as fitting a '36-'55 electric sender in a '35 tank, it may be "possible" but not worth the effort. You will need to remove the reinforcement around the current sender hole and resort to sheetmetal screws to hold the replacing sender in. This is asking for leaks. This is no adapter for adding an electric sender to a '35 tank that I know of.
Your BIG problem will be getting the neck off. Use lots of penetrating oil over a few days and use a spanner wrench (not a pipe wrench), to get it off. This may take several tries. If all fails cut the neck and rejoin with a rubber connector.
Hope this helps.
Tom