Thank you Rob, thats what I was thinking as well you say a number # 1 bell??? I thought a #2 was in order for the mack?? please more details on this if you would... In all the OTR driving Ive done over the years and Hauling heavy up to the North slope on the Haul road to Prudoe Bay, Ive never shock loaded a trans or broken any part of the drive train. anyways I do think the cummins would be a good choice but I hadnt thought of a dt466 I would like to know more of this as a swap, I will have to do my homework on this engine I know of it just dont know about it. Mine is a 1958 thermo, Has Horrible blowby although this is on some bad fuel last time I had her running, it does have a miss but seems to clear up some and dont smoke once warmed its not a compleate miss I think its hitting but not as hard as the rest on number 4 if I remember correctly, also after sitting a few nights during the summer with weather at about mid 60's to high 70's ALl i gotta do is turn the key and not hardly any any cranking its running mind you thats with old fuel I drained what i could out of the tanks and put in new and did the other start up things.. so not sure what to think about this as the blow by is so bad, It has been sitting for years till I got ahold of it. I cant do anything with it as of yet, I didnt get my shop compleated this past year, so its sitting inside a shell at about -30 below shivering and waiting for the weather to warm up so I can work on her... lol I havent found a rebuild kit that has new pistons that fit the Con rods that this engine is supposed to have,(ie. the 1.6" wrist pin)so dont know what to do there either other than get maxidyne conrods.?