stock gm roller cam setup in old block

I have a roller cam and lifters from a cracked 350 1 piece rear seal engine that i took apart. The new casting has mounts in the oil galley to hold a bracket to keep the roller lifters from rotating. I would like to put this cam setup into a old block withut hte mounts how can i make the mounts? They are around 1" high and 3/4 round. Can i just tap a hole in the block and put a bolt with a spaer under it or a just a stud with nuts to hold the bracket in spot. I realize an oil passage is directly below it so is there enough metal there to tap into and not have to worry about it breaking wile im taping it?
Can I weld onto a block? If so cant i just weld steel cylnders on to make the mounts?

This engine has the type of bracket im talking about http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33615&item=1876498861

I think you'd be farther ahead buying retro-fit roller lifters.

The mods you propose to the block are probably more expensive, and potentially a big problem. There is also machining to be done on the top of the lifter bores, I believe.