Sounds like you just need to refreshen the 383 in the truck, add some Roadrunner 383 mag heads with a 5 way valve job, new springs, a perfromance camshaft and rering the pistons with a good hone job and add headers, MSD ignition, big carb and alum torker intake, forget that boat anchor 413, waste of time and effort and money, you cant make a silkpowerpurse out of a 413 boar harelol Good luck, those motorhome engines are dogs when they were new....The 383 is already in your truck, tons of parts cheap everywhere and not rare. Sounds like you have a low compression 383 in the truck that needs to be wakened up!!!!!