Ridiculous project but is it possible
 

Hi. I have bought a mk1 lt35 van that my original plan was to fit a om606 in like my other car.. now it has already a very sweet d24t engine in it which after doing some research here looks an exciting engine.. so plans have possibly changed.. so I'm now thinking 12mm pump head. Bit of head work. Large air/air intercooler and probably hx35 turbo... question is how hard is it going to be to see 300whp.. I'm very excited about creating a flying brick and would love to use the d24t but if this power is out of reach I might go back to plan A.. I'm also fitting the volvo zf4hp22 autobox to get rid of the ridiculous gear ratios

You should reach 300hp with some good head work, large and effective intercooler, hx35 or similar, and built pump.
There is guys making ~300hp with the smaller brother to the d24t, the 1.6 4 cylinder.
The crank and block are very stout on these d24's. There is aftermarket rods available, I'm not sure what HP level needs them though. The biggest drawback to high HP is the cylinder head. The d24's at least started out with 2mm larger intake valves then the 1.6.
Sounds like a cool project. Let me know if you need the 12mm pump head!

That's great mate.. good to know. Will pm you for some prices