Engine rattles and loses power when throttling

My 1985 Dodge Ram 150 royal van (has a 5.2 L 318 8 cylinder engine), with 200,000+ miles on the odometer, has always seemed to run erratically. It had trouble starting and idling in gear and would easily "die" if put into gear before the engine got warm. Sometimes it would still die even if it was warm. So I borrowed some money from my dad to take it to a small, privately owned and operated mechanic my family has known for some time. He then adjusted the timing, changed the oil, and fixed some other minor problems that were preventing it from getting inspection passed. So it ran for a while, starting ruff and idling poorly in gear and coming to a stop, but it would get me around good enough. I used this van to do Red Cross volunteer work going on emergency response calls to help families who have lost everything in a disaster such as a fire, tornado, earthquake, etc. and it means so much to me to get it running again or replaced so I can once again return to helping people. However, about a month ago, when I was driving to the mechanic's shop (we are good friends and he likes me to visit and learn some things as I am mechanically inclined and I like helping people), all of a sudden it started "rattling" in the engine and lost power, esp at high speeds (60+ MPH). It also started "jolting" a little as I throttled it. So I had him take a look at it one evening and he made some fuel/air mix ratio adjustments to the carburetor and changed out the thermostat and replaced the radiator fluid. He also adjusted the distributor to fix the timing. However, upon returning home it once again "rattled" and lost power, and then it just wouldn't start or stay running, so an uncle of mine (he has mechanical experience/training) adjusted the distributor and timing and it started and idled more smoothly than it ever has but it still makes the "rattling" sound when throttling to get up and go. The more you throttled it, the more the "rattling" occurs. So we tried to once again drive it to the mechanic's shop (about 25 miles) from my house and this time the radiator hose "blew" and busted and fluid went everywhere, so my uncle who was helping me and following me helped me tow it back to my house and decided he would help me fix it instead. Today we removed the thermostat, refilled the radiator fluid, replaced the radiator hose, and changed the oil and oil filter but it still "rattles" when driven and starts losing power again. I don't know what the exact problem or even what some of the problems may really be, but I need help and would really like to return to "active duty" in the Red Cross, and it's very important to me and it's the first thing in my life for a very long while that feels important and means so much to me. Please help if you can...