The easiest way I have found is to have someone else do it! Ok, sorry, but I had to say it. They are a bear and it's acually easier to unbolt the core so you can get enough room to get the hoses on. But it can be done with it in place, just make sure the hoses are warm and pliable and use something like Vaseline on the hoses to get them on without damaging the core. I'd go the the trouble of unbolting the passenger seat to get some room, too. Good luck!
I would caution you on trying to remove the hoses without actually removing the heater core. I am actually in the middle of replacing my heater core, and I discovered that there were hose clamps inside the car holding them in place, so no amount of vasoline would have got them off.
On the 69s, at least without air (you didn't mention) you can get at the hoses without removing the core or splitting the case. Both clamps are on the outside of the case. You will have to remove the passenger side of the dash though, and it can be a real challenge to get the old hoses off the core. They like to weld themselves on there.
If you have air...prayers sent!!
I just did a bunch of dash work on mine, including replacing the old worn out fan motor. You need to remove the whole case to get at the fan motor. I would like to beat the engineer who designed that to tears in front of his kids. It's a hellish PITA, and they easily could have designed it to be removed from the outside.
I would caution you on trying to remove the hoses without actually removing the heater core. I am actually in the middle of replacing my heater core, and I discovered that there were hose clamps inside the car holding them in place, so no amount of vasoline would have got them off.
Actually, I assumed he would cut the old ones off carefully, the Vaseline is used to help the new ones slide on without damaging the core. But I agree that unbolting the core is best.