"I just got a Mauser M1908 and know ABSOLUTELY NOTHING."
How about starting by simply SEARCHING the forums, using the vBulletin Search function in the black bar, top right?
Enter
Brazil
Mauser 1908 and start reading.
As to your queries:
1) BTW, although the K98 has the same action length as the 1908, according to Kuhnhausen "The mauser Bolt Actions" p.214, the barrel ring is smaller (1.3" vs 1.41"). In other words, the cutout for the action is too small at this point. You are referring to the
K98k
, not the K98a, aren't you?
2) This sort of alteration - even if feasible - leads to a mongrel that is of zero value if you should ever wish to sell it. You are just going to FUBAR a rifles that, basically, just needs the PROPER stock to be refitted.
IMHO, just be patient and look out for the proper stock. Don't start on complex alterations that would spoil the rifle even more. I most certainly do not wish to offend, but if you have to ask how to do it, are you competent to do it? After all, you said at the start that you know nothing about this type of rifle - so start by reading the knowhow available, as recommended above.