]Since You Dont know the amount of rust or damage it caused to the cylinders, it would make more sense to pull it and at least do a minor rebuild. starting it now, could damage the block, and/or pistons. Truthfully, after being stuck, it is never going to run right untill the rusty cylinders are reconditioned anyway, so why tear it up, or damage potentially re usable parts?. Chances are, whatever valve(s) that were open have rust issues, and wont seal properly, or for very long. If it is the original to the truck block, I, personally wouldnt want to damage it. There are a lot of stroker kits being installed in otherwise decent 390s, therefore a bunch of 390 cranks and rods available. Have it bored to a 390, and put it back together. If you can find a known good 390 or 428 camshaft and lifters, they would add some zip to it as well. The 73-76 FE engines were performance slugs, due to emission changes to cams and cam timing chamges, So, even a rebuild with earlier, and fresh parts will leave a grin on Your face every time you hit the throttle. Again, try and resist the urge to fire it up and possibly ruin the block, and even the stock pistons, if they can be cleaned and re rung, at the veryminimum. No reason to spend a fortune on it, unless you want to, but, preserving it, and the accomplishment you will feel when its reconditioned, are priceless.