I think I'd avoid using Han Bespin's head for a Han Stormtrooper - the helmet won't fit, will it? Better to look out for a beat up, paint-worn pinhead (you won't want to pop a mint one) and repaint him.
I've made vintage customs I'm quite pleased with of
Tarkin (carved a beat up Imperial Commander and repainted it)
Owen Lars (Emperor torso, Han Bespin legs, Lobot head and arms - milliput hair and added detail)
Rebel Marine Trooper (Han Bespin torso and arms, legs and head from a Death Squad Commander - added detail and helmet modelling in milliput)
I'd post pics but my work laptop (my only web access) bars image hosting sites.
Customs also provide a use for the repro weapons that turn up in job lots off of ebay. A bit of silver paint on the tip and sight of a black repro bespin blaster looks perfect. My biggest problem is being colourblind - I'm told that the shirt on my Rebel Trooper is bit too blue and not grey enough. I was going for a bluey-grey, clearly...
Key tips:
1: if it feels too much like you're forcing the limbs out of the sockets then boil a little longer
2: Be patient cutting the connecting rod between the two halves of the torso
3: Mixing a bit of metallic paint in with base colours can make a bit of difference to how "fabrics" look
4: Keep spare limbs in a box. They may come in handy later...
5: Practice on scrappy figures you don't care about
6: Don't tell your mates in the pub. Unless they have been bitten by the bug, they won't understand...
I'm looking out for a beat-up, yellowed, paint-worn Luke Farmboy (i'll only cannibalise beat up figs as I'd feel too guilty) so as to nick his head for my work in progress Luke x-wing removable helmet. Bollux: once you pop off Luke Stormy's head, I'd quite like it (if you were going to bin it).
Scrap figures I'm looking out for:
Squid head
Hammerhead
Luke farmboy
Bossk
any imperials.