Irish Knots

Does anyone have any idea on switching out a stock on an Ithaca with an after market thumbhole stock? I really enjoy shooting a thumbhole stock - but unsure of how to do it is this a fairly simple job?
Does anyone know what manufacturer is close to Ithaca; is it Remington or Winchester etc.?

Just got a new piece of property - shotgun zone-want to get re-acquainted with the slug gun

Also, anyone have experience shooting slugs/sabots through this gun?

All input greatly appreciated!