So what will it take to reach 400

Pump work (fuel plate, AFC)
4k GSK
5x.012 injectors
62/68/14
18-20* timing

Should be a pretty good setup. You could do it on a stock turbo, but it wouldn't be clean or efficient. From what I've heard, the 68 turbine spools quick, but still keeps low drive pressure. Head work (resurfacing, o-ring, studs) would be nice to do, but I wouldnt consider it a necessity up front if you run a good turbo with it, keeping the drive pressure down.

How do you do the timing, whats the 62/68/14?

Do a search on timing, it shouldn't be too hard to find quite a few threads about it.

62/68/14 is a turbo size. 62 means that the compressor wheel (cold side) is 62mm. 68 means that the turbine wheel (exhaust side) is 68mm. 14 means the exhaust housing measures 14cm.

a smaller exhaust housing will be nicer for spool up and daily driving

That is true too. Maybe a 62/68/12.

yes it would be quicker I had a 62/71/14 on my 01 and it was a little laggy. better in compounds but not perfect

I have a hypermax turbo on my power stroke, will that be bigger/work on the cummins?

Ok found out my turbo is a holset H2e 63 72 17, is that going to be to big, have to much lag.

Is that the one off of the Ford? If you had a way of tightening up the exhaust housing it might work. If you could somehow get a 12 or 14cm housing on there it would work, but it would still be pretty laggy.

Then you still run into the problem of getting it bolted up to the Cummins, as it's probably not a T3 flange. But heck, if you've already got it it's not costing anything so you can't beat that.