h-beam rods if you plan to put turbo in or rev past 7krpm.
But, I have an idea, get Penta crank to your hands, marine AQ17X something can't remember full models, but those should fit, there were two kinds of them, for new and old B200/B230, switch was somewhere around 86? When they changed rods, bearings were changed that time too.
You can get more displacement and torque with one, that is if you can find one for not too much money.
2nd get 531 head, it is best from 8 valve heads, you can tweak 530 to be like 531, but when tweaking 531 it is possible to get lot more out from it.
Here those cranks cost anything above 1k and heads 1.5k upwards mostly, but in UK prices are lot less I believe.
If too costly, then how about taking bit off from head or block? More compression is always good, sure need to adjust spark and fueling too then, but those you need to adjust anyway if you change engine. Also get bigger valves installed and smooth out exhaust ports, also smooth intakes too, and match both to manifolds. Some 10 maybe even 20% gain can be gained from modifying ports and matching them to manifolds, but to get use of that gain bigger valves might be needed (not very expensive in machine shop, but sure costs something).
Read from:
http://people.physics.anu.edu.au/~amh11 ... 31_530.htm
Volvo 360GL -88 -under restoration-
Volvo 343DL vario -81 -running-

Volvo 240 Diesel -83 -undecided-
Citroen ZX Dturbo -97 -daily-

