1. I agree with trying to get a title from brother. It may be possible for the brother (or whoever got the truck) go to his/her DMV with proof of inherited ownership, get a title in his/her name and then signed it over to you. That still may be possible. In my state, on a old vehicle, DMV does not need to see the vehicle for that type of thing.
2. If that does not work:
The bottom line is you must find out what your state requires. Either by searching their website or going there and wait in line to ask your questions. DO NOT take any paper work with you or give any serial numbers with you and don't give personal info to the agent. Just ask what they need. A general question about buying a vehicle in X state with bill of sale only and getting a title in your state.
3. This has been mentioned also: Neither the deceased person nor the brother owned the truck if it never got transferred. So the bill of sale is no good. The owner is the last owner of record. If your DMV hears that whole story, you are in for a battle. You didn't say or maybe don't know if the title the deceased person had and lost was the title from the person he bought it from and never took it in, or it was a title in his name.
4. The ID plates and motor serial is great but the issue still remains. No title. BTW You did not say if you bought it in your state.
Of course as you know and we have said many times, it is not advisable to buy a vehicle without a title. States have different rules. Do the check BEFORE buying.
In my state a vehicle without a title is a "parts truck" to most people. It is VERY difficult to find a local buyer. The bonding proceedure is long, fairly expensive and risky.