Need some help with high torque 408 build

My truck is a W250, D60/D70, NP205. It's got custom spring packs and can carry about 3500lbs in the bed... Right now it's set up to plow but I also run wood and scrap with it and tow a car trailer. The 360 in it has an EX262, Performer 750 carb, MSD, and cheap headers. It idles for hours, rarely goes full throttle, and never goes over 4200rpm. There's "will rev" and "makes steam". This 360 will still make power at 4200.
I would expect you to have issues with detonation and making any power over about 2500 with that cam. Think about it this way: the stroke of a 440 is .370" or about 10% longer than a 383. The same cam in the 335hp 383 that made great midrange and top end was a stump puller in the same 375hp 440. The 4" stroke crank is .690" longer stroke or about 18% longer. Given everything else was the same, a 4" stroke engine should have 18% more cam and 18% more carb. In this case that would be 708cfm carb (assuming you run a 600 carb on a 360...) and .483 lift with 240° @ .050 (assuming you have the stock '77 4bbl cam that is 203° @ .050 and .409 lift going off Rock Auto). That should give a similar power curve to the smaller 360 but will have higher peak figures and those figures will be lower in the rpm range than that of the bone stock 360.