Right up front please accept my thanks for the advice provided here. I appreciate the time spent to reply to my inquiries. Now to my current thoughts and questions.
I am about to begin the processes of putting an orange shellac finish on my 1893 Parker GH forend. My goal is to create a finish that is close to the original as I am able to accomplish. To this end I have accomplished the following. Mixed my own shellac in the these cuts and colors: 1# Plantina, 2# Blonde, 1# Orange, 1# Garnet. These are ready to be used if needed. I have BLO available, but not raw LO. I have Japan Dryer available if needed. I have caster oil available if needed.
After extensive reading I have decided that the technique of french polish is not required to apply the shellac. I will use a pad as in the french polish technique but will not be building up a gloss finish. Also, I will not be filling the pores in the walnut. I examined the wood on the Parker stock and the forend before starting the project and I see no evidence that filling the pores was part of the original wood finish process.
I have read the two articles by Austin Hogan (thanks to Mike McKinney at the PGCA for getting the Parker Pages USB to me in a timely manner) and I have consulted my gunstock finishing library works by Newell, Dunlap, Mills and Barnes, Howe, and modern texts by Flexner, Jewitt, Dresdner and Allan and the excellent collected work by Woodreaux (DoubleGun forum). This is what I have gleaned to date.
Hogan, through his experience as Parker collector and editor of the PGCA publication 'Parker Pages', along with material published in Chapter 10 of the Parker Story believes that a shellac finish was employed by Parker in finishing gun wood unless an oil finish was requested and only on higher grade Parkers. He does not provide any real details as to the exact process. I do not have a copy of The Parker Story and do not know the level of detail it contains.
Newell recommends the addition of caster oil (non-drying oil) as a plasticizer to the shellac.
A discussion on the Wood Web states that boiling raw linseed with shellac to produce a varnish, but this is not what I understand Parker would have used. A contributor to that discussion also states that mixing BLO and Shellac is not to be recommended. https://www.woodweb.com/knowledge_base/Shellac_and_Linseed_Oil_Finishes.html
Mills and Barnes recommend the one-time application of raw linseed to the stock prior to the application of shellac. I see no evidence that the Parker wood was colored with linseed oil prior to application of shellac.
Dunlap gives his favorite technique of applying BLO to the wood following by shellac immediately and the use of the hand rather than a pad. I do not think this to be applicable either.
Howe has a strong distaste for "that orange shellac, colorless, dreadful, frightful looking, ... disfiguring looking finish" In a word awful, do not use.
Flexner, Dresdner, Jewitt, discussing the application of shellac to wood finishing in general, each recommend mineral oil as a lubricant and not linseed oil. None recommends a direct mixing of linseed oil, raw or boiled, in any proportion with the shellac. Oil only as a padding lubricant.
If you have direct experience with using shellac as a finish on a Parker (any gun wood) and not building up to a french polish technique finish and could provide a photo or two of the Parker wood I would be appreciative.