That 90 is as perfect as they come. From the photos it looks like it had been stored really well. The first thing I look at it the floorboards.
Yours have absolutely no surface rust showing which is huge.
If the motor is stuck it is still a good idea to split the case since the seals are likely dry .
Before you give up on the motor try to unstick it.the rings may just be stuck.
Remove the plug, pour a couple or ounces of Marvel Mystery oil in and let it sit a few days.
Remove the fan cover put a socket with a breaker bar on the nut and rock it.
DO NOT TRY AND BREAK IT LOOSE WITH THE KICKSTART LEVER.
Also, drain the oil from the gear case and check for metal chips and if it smells like old gas.
PM me your mailing info and I'll send one of these stickers.