New member-drivetrain questions

[NeedATruck]

Hello! I am new to the forum and considering a 67-72 Chevy or GMC in the future. My desire is a 4WD, either pickup or Blazer, but I have some questions on how the 4WD in the K20 functions, having just enough experience with older 4WD trucks to be dangerous.

How exactly does one go about engaging the factory 4WD system? I know that electronic shift on the fly didn't exist back then. Can the transfer case be engaged completely from inside? Do you have to get out and manually lock the hubs or are they already locked? If you don't have to get out and manually lock the hubs, can the system be engaged while the vehicle is in motion at all or do you have to be completely stopped?

How robust is the factory transfer case? I don't plan on doing any offroading, but do tow a boat with my current truck. My plan would be a mild LS, 400-450 HP. Would any upgrades to the factory drive-train be warranted at this power level? I assume the rear end and trans (I'd probably use a 4L60E or 4l80E) would be fine, but don't know about the transfer case and front axle.