smallport heads have an external oil drain from head to the block, the 20v doesnt. this could be an issue.

besides i wouldnt bother with a combo like this, as the silvertop and 20v bottom ends are VERY similar in strength. obviously the pistons are different, and the silvertop rods are the same as GZE, but its not worth it.

just a buy a complete smallport, or complete silvertop, save yourself the hassle of combining the two.

just my 2c.