MM, don't know what you mean by "figure the pull at clew, tack, and head of sails"… Are you trying to find loads for running rigging?
What's your budget? Do we get to outfit a 25 year old cruiser with high tech racing lines?
I'm assuming for a cruiser like a 222, you'll probably want to go somewhat budget. If you're racing that 222, good on ya, but you probably aren't.
I'd use 5/16" (8mm) New England VPC for halyards. Original spec for an O'day was probably 3/8" (10mm) double braid polyester, but the VPC blended core should have less stretch. The site store specs 5/16" Sampson XLS, but I would NEVER use poly double braid for halyards, it's like trying to tension rubber bands.
For sheets, I'd go with 10mm double braid polyester such as New England Sta-Set for your main, and possibly 8mm for jib sheets. The running rigging calculator here in the website store specs 5/16" (8mm) Sampson XLS, which is also a double braid polyester. I personally like a larger line for the main sheet, and a slightly smaller line for the 110% jib, so that the lines aren't quite as heavy hanging the jib in light wind.
1/4" (6mm) VPC is probably fine for your control lines for the main, such as outhaul, downhaul, and reefing lines. Nettles, the lines that tie the excess sail to the boom when you are reefed can be any 1/4" soft polyester line.
There are less expensive double braids, such as Novabraid, available from Sailcare.com.
I, myself, appear to have more money than brains, and I have 1/4" Vectran cored halyards, and 3/8" and 5/16" New England Salsa line for sheets. I use 1/4" VPC for outhaul and reefing lines.