Can someone recommend a gunsmith who has had experience converting  old Winchester low walls from rimfire to centerfire?

I would also like to to reline the original barrel to 25-20 Winchester.

Any information or advice would be appreciated.

Just did one last week, went from 22LR to 45 Colt.  Not to hard to convert the firing pin. This one just needed the hole plugged and a new hole drilled in the right spot. The pin was offset from the main body so I just cut it off and drilled the body for a new pin in the center. Used a piece of pin stock for the new pin. I can also do the liner for you.

What Ken said!  

I tried going with a plugged .32 rf block and a cf pin on the first of these same conversions I did and found the new fp hit low on the primer, leading to the occasional misfire.  That one was fixed by using a longer link which in essence raised the whole block by the necessary amount.  This involved some geometry, and left the block's upper edges looking a little high, but worked well.  

As mentioned by David, replacing the block is the most straightforward and simple method, but if you commission the whole job done at one time (rf to cf and barrel lining) by a single, knowledgeable gunsmith such as John Taylor who has just chimed in, all of these pesky little details get worked out before you see the finished product.

I have no direct connection to either David nor John, knowing both by reputation only, but those reputations would certainly lead me to take advice from either or both on this, and since you don't know me either, I'll just say that the three times I have been in on this exact conversion involved bushing the block on two of them and replacing it outright on the third... and all worked satisfactorily with the adjustments mentioned.

HTH ~ Froggie

PS  The .22 rf block already has the fp on the proper elevation, so no change of link, etc, is necessary.  I have no experience with rf blocks for larger calibers such as the .44, but they come along so rarely they shouldn't present a problem.  The .25 rf, if encountered, will probably be close enough to centered without adjustment, but YMMV.   
GF

Reply sent.

David