I don't own any Lee-Enfields and have never studied them, but I would suspect that they had the same general attention to detail put into them: the British could not produce them fast enough to supply their own troops and were desperate for rifles as WWI & WWII settled into their long stalemates.
I guess that the reply to Steve M should emphasize the idea that it's a little too optimistic to expect anyone to know if a Brno 08/34 would accept aftermarket parts when all Mausers in general take some close looking and usually some fine fittling to modify with new parts. About the best one can say is that it should be a very standard large ring Mauser and present no unusual difficulties that could not be solved by a decent gunsmith.
I've been working on a Turk 03/38 Mauser I picked up earlier this month. I bought it because it has a nice fiddle back stock that must be real Turkish Walnut and it seemed O.K. in the other departments as well. This was made at Mauser Obendorf itself and should be about as standard a Mauser as they get, as it was made when Paul Mauser walked the floors of Obendorf himself. The action is very smooth on this rifle, which I attrribute to the Germans, but the Turk reworking is a little on the poor side. The action is inletted into the pretty stock in a very loose manner and maybe it would benifit from rebedding, but I will shoot it first to see about this. The trigger guard must be from another rifle (they ground off the serial numbers) and the floor plate doesn't really fit right (hard to get off and on).
Last night I was working on the steel butt plate, which was oversized and hardly fitted the end of the stock, obviously from yet another rifle. It's a pain to make those things fit right with their multiple curves. Dakota Arms charges $500 for a nice checkered steel butt plate and $600 for a skelletonized one: as much as a whole Remington or Winchester Rifle and quite a bit more than a Savage! So you can see how costs take off like a rocket once you start to get critical of all the little details and start demanding that which requires skilled, careful handwork!
Don't think that I don't appreciate what modern manufacturers are doing for us. Thanks to the appearance of modern CCN machining, arms that every one even twenty years ago would have believed to be impossible to produce at anything resembling an affordable price are now being produced at prices that are more affordable than ever in history: Modle 70's, High and Low Walls, Rolling Blocks, Sharps, Trapdoors: the list goes on and on. They can give us the basic rough actions now, but if you want the fine details you have to get it done yourself.