The 387 HP number seems believable or close, it really depends on the head flow. I would expect more like 350 but if the heads are flowing really well, sure, 387. I would believe 460 HP on a smogger bottom end too, I would just expect it to have heads and a cam that would support 500 HP on a built bottom end. I'm stating the obvious here but a given compression ratio doesn't mean that the engine can't make XXX power, it will just make less than if it had more compression.
If you take a smogger short block that is in good working order with good ring seal and put a great set of heads on it along with a good intake, headers, and the right cam for the application it is going to make impressive power. It won't make as much as a 0 deck, .040 quench, 11:1, freshly machined and torque plate honed engine with forged pistons and H beam rods and all of the other racey stuff, but how much power does that all add? The pistons and rods are worth nothing really, the 3 point CR increase, quench, and better hone job/ring seal I would guess 30-50 HP on a 500 HP engine. One point of compression is supposed to be worth up to a 3% HP gain, but that relationship really isn't totally linear. (I.E. going from 11:1 to 12:1 will not create the same gain as going from 7.5:1 to 8.5:1).
When you start with a smogger bottom end the combo will be more sensitive, and the low end torque loss will feel exacerbated by both the even lower dynamic compression and the fact that the engine started with less to begin with. The worse your starting point and the bigger you go with the cam the easier it will be to turn it into a turd. Those engines will want more timing and more aggressive ignition curves too. Also its worth noting that a smogger 454 truck engine also has peanut port heads which leave a bit to be desired vs passenger car oval port heads from an earlier big block chevy, so there's more to it than just CRs dropping for some of the smogger engines. What was in the 400? If it was a 509 cam with manifolds and a stock converter I wouldn't expect much from it, but you'd probably get away with the same parts in an earlier 440 and still run respectably.
Here is some reading from this board on smogger combos;
https://board.moparts.org/ubbthread...45/fastest-stock-smogger-360-combos.htmlhttps://board.moparts.org/ubbthread...-stock-smogger-440-bottom-end-times.html
