One way to look at it is what have you got to lose by trying it. The gears are definitely in bad condition and will further continue to self destruct. But if you only plan to putt around with it a few hours a year at shows, they could last a long time.
The deal breaker for me would be having grooves in the axles where the bearings ride. Replacing the bearings is good insurance, but if the axles have grooves, they must be replaced or repaired for proper bearing support and operation. More money!
Since the price and availability of the gears, axles, etc. has escalated, a good used transaxle can be money well spent. I personally would look for a good one from a 200 series. Less age doesn't always mean better condition, but odds are better for getting more salvageable parts from one or two. Watch for bargain priced ones and don't expect to much. Just a back up for the future. Shifter, brake parts, pulleys will need to be swapped from the RF tranny to later models.
The RF manual suggests 3 pints of gear oil for the tranny. To get it right, expect to have the tranny installed in the machine and fill to the level of the front (fill) pipe plug. 80w-90 is probably what you want, but others use heavier (140) in warmer climates.
tommyhawk