Jim, having quickly reviewed the rule book, I can't find a definitive answer to this, so I will go straight to you (knowing that you probably won't see it until you get back from E-G.)    
Would it be acceptable and "in the spirit of the rules" to use one of those shoe-type arrangements on the fore end of a sporter type or classic target type rifle when firing from bench rest?  What I have in mind is one like Sinclair and others sell to provide a better surface to use with your front bag.  I recall that Charlie Dell and others have made up similar devices to fit the butts of radical schuetzen stocks (especially German ones) so they would work better on a rear bag, and that got me onto the current question.  TIA for a definitive answer, so I can continue with or abandon this line of inquiry as appropriate!    
 
Froggie 
 
PS  The stimulus for this question was the one by Brent about length of a fore end, but I thought this detail needed a second thread rather than hi-jacking his.    

Brent, the specific application of the butt stock that I was referring to was an original German (Beuchel Meister, perhaps) that CED wanted to try off the bench for some reason.  It was equipped with a rear sling swivel, as memory serves, so he used that hole to mount a shoe-like affair that was carved inside to fit the toe region of the stock and left pretty square and flat-bottomed on the outside.  I know he used it for testing the rifle, but I don't know whether he or anyone else used that particular one in competition.  I seem to also recall that he made a similar adapter for his pet offhand rifle built on a Peregrine action and he DID use that for at least one or two bench competitions in the latter days of his shooting career.

Froggie

Herr Frog;
I don't have my rule book ar hand but Having contemplated this very thing, it seems to me such a device would have to be made of wood. As a matter of fact i saw a Ballard on the line yesterday with this type of "adapter" added to both butt and forend.

Some of these rules seem a little ridiculous compared to modern striker-fired astions in one piece stocks but who am I to say?

Sure the forend thing is OK! If a slide is OK why wouldn`t it be!
Yes you can add the what ever you want to the butt stock!
Jim

But Frog:

Section 2.91  Page 12 Rules book,

A sandbag or shaped rear rest sand filled bag made of leather or canvas may be used under the toe of the butt stock.  No other device or support is permitted for the toe of the rifle. V-blocks or rests, guides or ways, or any such devices which might aid in alignment of the rifle, are prohibited. An anti cant device (bob sled) similar to the Pope style muzzle rest or the one descriped in Mann's book is pemitted.

That mean to set the butt stock on! You can add wood to the stock or add the device to the forend is legal!!!

At least 2 regular shooters at EG use rugers that have flat bottomed "sleds" added to their buttstocks.  Both use notched out wood blocks to provide a broader based surface.  One is closely fitted with glass bedding to fit the stock and is then attached with industrial strength double stick tape.  The other is screwed on using the ruger rear sling swivel screw hole.
Over the winter off-season I am planning on making one for the rear and one for the front on my Ruger bench gun.  As I recall there is a 2" max width on forends, not sure about width on the butts.  I'm planning on using machine screw inserts on the butt and weighting the "sled" the forend will attach through existing palmrest holes and may or may not also be weighted.