The old Infantry Tactical Doctrine Pam 2 (Fieldcraft Pam) used to have assembly of webbing, it was 58 pattern, but the last Pam 2 I saw had 90 pattern.
I don't know if the latest fieldcraft Pam still has webbing construction in it, or if it is just Battle Lessons and Exercises these days.
May I make a suggestion though, don't use PPT for this type of lesson, you would be a lot better off getting your hands on a couple of sets of webbing and a couple of troops to assist you, breif/rehearse your troops before hand and you narate the lesson as they assemble their webbing.
kev do you happen to have a copy of the infantry training pamphlet? as i need to put together a lil aide memoir for a few of my lads and the cadet training manual is gash. if youve got a copy you could email me it would be much appreciated!