Off the top of my head.....
The
289 HiPo (also called the "K-code") differed from the standard 289 in that it had a 'hotter' camshaft; solid lifters; smaller cumbustion chambers (which, if I remember, gave it 10-1/2 to 1 compression); HiPo exhaust manifolds (like cast-iron "shorty headers"); a 595 (
not a 600) CFM Holley carb with manual choke; dual-point distributor; and other stuff I'm pretty sure, but I forget.
The
Boss 302 obviously displaced 13 cubic inches more than the 289 HiPo; but it also had a 4-bolt-main-bearing-cap block with thicker block deck and cylinder walls, and a higher content of nickle in the metal It also had a forged crank and forged rods. I
think it had the dual-point distrbutor and a bit larger Holley than the 289 HiPo, but I may be wrong.
The biggest change was that the Boss 302 used cylinder heads with
canted rather than
inline valves - what most everybody calls "Cleveland heads" because they were pretty much the same heads used on 351 Cleveland engines. They "breathe" better; so more air/fuel in and more HP out.
If I forgot anything, or screwed up somehow, somebody please correct me.