To loosen and free the very worst of rusted parts I swear by Aero Kroil penetrant by Kano Laboratories -
http://www.kanolabs.com/Aero Kroil penetrant is a tremendous aid to liberating galded and seized parts.
Ask Allan Landry what he thinks of Aero Kroil.
Silicone spray might be worth a try in removing side covers.
Wayne, always try sourcing through Honda before paying excessive prices on ebay or elsewhere. I have been recently able to obtain most any engine and chassis parts, exluding such items as gauges, fenders, tanks, etc. Items such as new side cover grommets, no problem.
Looking at your sandcast webpage, picture appears your petcock is the early short neck. As far as we have been able to observe, the last frame vin for the short neck petcock is 1937.
It's interesting, your tank is the 17 litre later type........ Interesting, because if Steve Frampton sees this and can jump in, if i remember correctly, his #745 has a 19 litre tank on it.