replacing pressure treated 1x4 boards on roof with non-pressure treated white pine - OK?
Keep in mind that those boards that you see under the plywood sheathing were originally spaced out as they are so that they could accommodate the installation of either wood shake shingles or tile type roof. The boards were surely never treated lumber at the time your house was built 85 years ago. (1935 places your house build in the pre-WW2 years). 

The most common lumber used at the time was rough sawn and may very well have been more than the standard 3/4" thick. White pine boards should be fine for replacement being as you are re-installing plywood over them. The white pine boards may very well not have the same strength as the original lumber but the plywood can take care of the difference. The difference in thickness should only be a problem if a plywood splice happens at the same rafter where new and old board butt up to each other. It the thickness difference is significant you may want to shim under the new pine board where plywood splices may occur. 

Note that it has been my observation that roofers that are covering spaced board with plywood sometimes do not put much energy in trying to splice the plywood on the rafter centers so shimming may be a moot point if you are following that scheme.