Lots of questions. Do you know the manufacturer of the drums?
Should the drums be turned or replaced?
This is somewhat subjective. Are they corroded or cracked or scored? If so, have a brake shop check the diameter and turn them if they are under the maximum diameter marked on the drum. Also check the armature (the flat inside surface) that the magnet acts against. If it is warped or scored you may want to replace the drum.
Where do you get them?
Do a web search on the name of the brake manufacturer. I don't have a '75 Overlander, but some of the manufacturers are Dexter (www.dexteraxle.com
) and Reliable Tool (www.reliabletool.com
You can also order parts from Low Cost Trailer Supplies (www.lowcosttrailersupplies.com
What are the proper size drums and spindles?
Either take the old bearings to an auto or trailer parts supplier, or buy a cheap caliper and measure them. Once you have the dimensions you can find the proper bearing sets at Low Cost Trailer Supplies website listed above.
What are suitable bearing replacements?
Some people will only use Timken bearings. Otherwise you are probably going to get Chinese or Eastern Bloc bearings. Matter of personal preference, cost, and the fact that probably 90% of the trailers on the road today are running on non-Timken bearings.