Right now I would be happy if my Om603 is running OK in my w123, but for the future, I might want to take the 'Finnish route' : more horsepower

250-300 HP would be OK I guess, but WHAT and HOW MUCH is needed?

I already know that I need, beyond 180 HP:
-modified injection pump with bigger elements, lets say 1000 euros
-good intercooler, let say 300 euros
-bigger turbo and bigger exhaust

What turbo?
Holsett?
Which type?
HX40? HX50?
Why that type for 250-300 HP? (spool-up etc)
Are there any 'subcategories', or are all the HX40 turbos exact the same

And to fit a bigger turbo, what exhaust manifold? Can I keep the original manifold and achieve 250-300 HP?
Or what modifications I have to make to adapt a bigger turbo (Holsett or another brand) to the original exhaust manifold?
Pictures maybe?

And where to buy that bigger turbo, at what price? New / secondhand?
Or can i buy such a turbo 'locally' because its also on some sort of small dieseltruck, that also runs in the Netherlands?
Ebay?

What size exhaust system would I need? 3 inch?

A lot of questions, hope someone can tell me some answers!
thanks in advance!

Forgot to mention:
I DON'T need 400 or 500 Horsepower!

250 (300 maximum) would already be OK

Today contacted a turbo supplier in the Netherlands, and he offered me the folowing HX40 (after speaking with the Holset firm):
60 mm. Inlet wheel
65 trim turbine wheel
17 turbine housing
wategate set at 1.88 bar.

Part number is 3539635, and he can offer me this one, brand new, for 914 euro.


Can anyone confirm this is the right one?
Price seems to me OK, or is it to much?

And IF its the right one: can i bolt it somehow to the original manifold, or do I HAVE to make a custom manifold?

And in case of custom manifold:
Can anyone tell me how mucht they cost if I buy them in Finnland?
Or maybe some pictures, and specs of the steel thats used?
Friend of mine is proffessional TIG welder, so welding wouldnt be the problem.

Turbo:
For a 250-300hp goal HX40 is overkill. Maybe HX35W or Schwitzer S2BG (fits directly to stock exhaust manifold) would be more practical solution. 250hp can be done with HX40, but general driveability won't be the best available. S2 is enough for 350hp with 60mm turbine wheel...

Exhaust:
3" is enough for 400hp+, so shouldn't be a problem.

Wastegate:
Both turbos are available with integrated wastegate. Easiest way to work with stock exhaust manifold.