Depending on how tight the bolt was when it was last torqued, I say you would need at least 200-250ft*lbs to get the crank bolt off. As the the cam bolts you can use the existing heads of the bolts, which fasten the cam shield plate right behind the cam pulleys between the pulley's spokes, as anchors to the bar to hold the cam still. For example, I used a 10mm socket on the end of the long socket extension and place the socket between the pulley's spokes and on the cam shield plate bolt, as if you were to remove that bolt, then firmly hold the socket extension while undoing the cam bolt.
Some old school mechanics (including me prior to having air tools and desperate) used the starter to crank and undo the crank bolts. I don't advocate this method but I performed a few times as a last resort so here it is but you're responsible for all your actions: use a long breaker bar with the bolt socket attached. The breaker bar must be long enough to lean against a sturding fix point to hold the bar/socket still when you crank the starter. I used mother earth as that fix point. Use that socket/bar to manually crank the engine clockwise (when view from the front) until you cannot crank further and the breaker bar rest upon the fix point you selected. Then get out of the way and give the starter a short 1/2sec crank burst and hope for the best. Starter method only works if your engine rotates clockwise (when view from the front) when run.