redrider,
If you haven't read this, it is an article by a guy named Rick Sieman about how to prep a cr125m for racing:
http://articles.superhunky.com/4/37. GREAT info. for somebody racing a vintage 125 Elsinore. Rick Sieman thinks the pegs welds are ok on the 74 and 75 Elsinore. I disagree, but don't know what to do about strengthening other than welding again or putting some kind of gusset to reinforce the peg area.
As far as a front wheel, if you want to keep costs down, the front rim on the mid 70's TL125 Honda Trials bike used the exact same rim as the 74 125 Elsinore. The center 3 digits on the 74 cr125 front rim part number are 355. 355 indicates a tl125. The part numbers are exactly the same, as they shared that rim. Don't even try to find a rim from a 74 cr125. Well, if you must have one off of the cr125, I can give you several cracked ones. Since it's the exact same rim, obviously you will have a much better chance of find a good front rim from the trials bike than you would from the motocrosser. By the time you get well into this build, it's somewhat likely that you may want to use the trials rim with larger spokes, at least until you decide you definitely want those expensive Excel rims. Sieman does recommend the next larger size spokes though.
Mark