quickchicken

i havent had any issues doing heater cores, and that top bolt aint squat if ya have a flexi-extension or 2.
i can do one in 45 mins and that includes gettin out the tools and putting them back up. i yse a pry bar to sorta break loose the hoses so they will come off easier, plus if i break the core coming out it dosent matter as its gone already. i also have someone guide the tubes towards the holes in the firewall with an extension or something of that nature so it will pop in easier.
i will say i do get a fair amount of those minor lil scrape/cuts when doing heater cores.

GearBreath

When I did mine, I had to take the whole dash loose to remove some broken flapper door parts, which I needed to replace while I was in there. The job is not difficult, just time consuming.

I have heard of guys that tried to shortcut removing stuff, and decided to force their new heater core in at a sharp angle and cracked the soldering around the hoses. If it won't go in, don't thrash it, or you'll have to re-do it. Also, some of the heater cores have very flimsy build, some are better. Look them over before you buy. If it looks flimsy, go somewhere else, or you'll be redoing it.

Good luck
GearBreath
So Cal