With my current aluminum combustion chamber, the compression ratio is adjustable up to about 18:1. That's the 'trapped' compression ratio after the exhaust port fully closes. The overall CR between BDC and TDC is adjustable up to about 27:1.
I suspect the 18:1 'true' CR is not high enough to burn pump diesel, so I think a new, smaller, cast-iron combustion chamber will be one of the next parts I make.
I may, alternatively (or additionally), add some diethyl ether to my diesel; the autoignition temperature for diesel is 410F, whereas it's only 320F for ether, so it should be able to run at a lower CR.
I'm a bit worried about going to a full cast-iron piston for vibration reasons. Don't really want to chop up my brand new race crank to alter the balance factor, so I'm hoping that I can get it to fire up with the changes I describe above before having to remake a piston.
Highest stressed components probably won't be the case bolts, so no need to do anything drastic like welding them shut. Pressure spikes in there won't be much different than a regular 2T motor. Thing I'm a bit worried about is the head bolts stretching, causing a leak at the head/cylinder interface. I drilled out the cases for larger bolts in hopes to mitigate some of those issues.