Working backwards from the wheels to the transmission.

1)Wheel adapters are not recommended for high performance aplications. Off-road racers especially take a beating and adapters are not designed to take the extreme abuse. Adapters also change the actual wheel off-set. Therefore, the wheel bearing load is also changed. Keep stock inside wheel dimensions for best results, and minimum wheel bearing wear.
2)Axle tubes Later model bugs ('66 and newer) have the transmission flange ends slip fitted and welded into place. Earlier models had only a butt - weld. (Except for the transporters.) The earlier axle tubes are also of a thinner gauge materials. The transporters were beefier but won't interchange with the bug. The transmission flange joint should be welded on the inside to insure greater strength. The second weak point is the fact that the tubes also bend easily in off road use. The outboard ends can be strengthened by using slip on tubes such as those made by Sandmaster, or if you like a set could easily be turned out in your workshop. Make them to fit snug and if you want you can incorporate a flange to reposition the rear shock mounting point, or add extra shocks.
3)Axles Stock axles are fine with stock engines and normal street use. In racing situations certain changes should be considered.
A)The stock axles are limited in their strength and durability, therefore an all out racer should be equipped with the heavy duty replacement type, such as those made by Crown or Sway- Away. These axles are uniform in density, are beefier, and are not dotted with blow holes. Some are even magnafluxed , shot peened and polished.
B)Stock axles can be improved upon by grinding and polishing the blade ends. Remove all sharp corners, polish and shot peen. Rounding off the sharp edges on the axle spade, reduces the chance of cracking and breaking occuring due to the force of the fulcrum plates against the sharp corners.
C)Remember '66 and earlier axles are of the short type, '67 '68 are longer (gives approx. an extra 2" track).
D)Transporter axles. Some off road racers prefer transporter reduction boxes. These provide both a lower final drive ratio and added ground clearance when turned downward. Several ratios for these units are available. The earlier units had a 1.4:1 (pre '60). Later models used a 1.38:1 (an optional lower ratio available). Pre '60 boxes are huskier, with heavier struts and external bearing boss. The gear sets are interchangeable from '59 on, (except for '63).
4)Fulcrum plates The fulcrum plates act as bearing surfaces for the swing axle type transaxle. These plates are under a great deal of pressure and their polished surface is prone to gauld as the gear lube is squished out. New fulcrum plates can be obtained that have oil grooves which will help eliminate this problem. Check size and clearances before you try to change plates.
5) Trunnion gear shafts and gears are subject to heavy load. Porsche
gears are huskier and have wider teeth. Best of all they are interchangeable without modification.
6)Differential.
A)Stock - the stock carrier can be beefed up to a point. After thorough inspection for cracks the stock carrier can be fitted with a kit (such as Crown's BEEF-A-DIFF) which provides extra spyder gears, shafts, junction block, and locking pins.