I have to say - much of your post doesn't seem to mesh with reality too well.

First of all - the pistons. B20 blocks are (generally, they vary) thick enough to overbore approx 3mm and put in B21 pistons, not overbore 6mm and put in B23 pistons. I don't know the differences between a B23 piston and a B230 piston, but either way 96 mm pistons are never going to work. Unless you completely cut out the old bores and welded in some sleeves. And no one is going to do that for you. I haven't a clue as to how thick the cylinder walls are on a B30 block, but they are PROBABLY similar to a B20. If you do go with a B21-sized overbore, you will need a special headgasket. KGTrimning is the only place I've ever seen big-bore B30 gaskets sold.

Then there is the line of thought that the walls of an B20 block bored to B21 size are a little too thin to handle boosted applications. So if you are really planning on forcing some induction on the engine you might want to leave it at 89 mm with nice thick walls and spend the money on the cylinder head flow instead. If you plan on really high boost, maybe some custom pistons and rods, although I'm not sure how much abuse a B30 crank can take.

Of course, increasing displacement means that to get the extra power from the displacement you need to move more air though the cylinder head. And the exhaust ports on a B20 are the most restrictive point in the whole system. With a stock head on a big-bore engine will gain low end torqu, but the torque advantage will fade as the revs rise and the peak HP won't change much if at all. However, B30 heads have different exhaust ports, round, and a little higher up (I think) - perhaps they aren't as bad as a B20's? A header and large exhaust would help, KgTrimning sells B30 headers too. They also sell modified B30 heads and cams too, but they are far from cheap.

I think the flywheel on a B30 is already fairly light, at least compared to the B20's. Wouldn't hurt to have some easy weight take off, but I wouldn't worry too much about it.

As for fuel injection vs. carbs - I think you are going in the wrong direction there for performance. A couple of SU's on a B20 can handle some HP increases, but I'd have to guess they are going to fall a little short on a warmed up B30. Fuel injection is a better way to fuel the engine. The problem is that D-Jetronic isn't very adaptable to engine hardware changes at all. You can tweak the fuel pressure up a little to give it more fuel, but for a really good solution you can use most of the D-Jet hardware with a programmable Megasquirt controller that can actually properly feed the engine. You could probably put MS on a complete D-Jet B30 for around $400 (rough guess).

John Parker's supercharger system isn't built for B30's, just B20's. I don't know if it would have the capacity to blow a decent amount of pressure on a B30 or not, but it wouldn't bolt right up to it in the first place. The price list for the B20 version with a single big DCOE carb feeding it is around $3500. It doesn't use the SU carbs, just the B20 dual SU manifold.

Cost for a complete engine rebuild will vary drmatically depending on what you do yourself and what you have done by a mechanic or machine shop. Good machine work is not cheap any more.

As for trailing arms - do yuo mean replacements? Just get some from a junkyard. If finding '75 164 rear suspension parts is difficult (I could see where it would be) see if early 240 parts owuld work - from what I understand the '75 164 got the 240's suspension.
--
I'm JohnMc, and I approved this message.