ok for those that are interested
i picked up 3 different front k frames today. the original 4k one, a sprinter 4age one (they are basically the same chassis so will bolt right in) and a s13 one. The s13 one is very close to the 4age one, in fact with very slight modification it will fit, i haven't tries to test fit yet, but looks like 1mm elongating of the holes that connect the frame to the chassis and she will fit.
The s13 frame will however sit the engine further back, it is obvious just by looking at the differences. This could be a positive and/or a negative in my case, as it will give better weight distro if she fits all sweet, but because i am running a fwd head i might need that bit of space between the firewall. I know the ca18det fits in there all sweet with the s13 rack as a mate just finished his. But the bellhousing on the sr box might also cause trouble. But meh this is what a mock up shell is for.
The mounting points for the lower control arms are also further out, which honestly suits me fine as i want more neg camber. The other good thing about the s13 frame would be running the s13 power steering rack. I am not sure as to the lock differences but s13's have a lot of lock standard so this rack might suit me better.
so this week ill cut of the 4k mounts on the 4k frame and get them rewelded at the same angle as the s13 one. i will also test fit the s13 from on the mock up shell. My engine hasn't landed yet so it will slow the box mating process down a little. Sooo annoying as i had an empty sr20ve block sitting in my back yard and i let my dad scrap metal it. Damn that would have come in handy now.
if people are interested i can post pics of my findings