As noted, I think the changes to the D jet controllers were related to the change in the cold start system. There are different throttle switches for the D jet system and I don't know whether they were product specific (VW versus Volvo versus ..) or whether they changed through the production run. I know some had over run shut off and some didn't. There are also differences between the MAP sensors; but, I don't know how that altered the fuel delivery.

Your approach to adjusting fuel pressure to adjust the fuel mixture won't work very well with the Bosch fixed fuel pressure regulator. The original base pressure on the B20E was 28 psi. At wide open throttle the manifold pressure will be about 14 psi absolute which results in an injector pressure differential of 14 psi. If you crank the base fuel pressure up to 35 psi you will have a pressure differential of 21 psi. You will have increased the fuel delivery in each pulse by (21/14)**0.5 = 22%. I would expect that you should be running rich based upon your modest 5% capacity increase. At idle, a B20E with a D cam runs with a MAP pressure of about 7 psi absolute. The injector pressure differential with 28 psi fuel pressure would be about 21 psi; but, would be 28 psi with your 35 psi fuel pressure. Fuel delivery at idle will increase about 15% so you still should be running slightly rich.

The engine coolant temperature has minimal effect on fuel mixture at operating temperature. It provides enrichment when cold and some people have added constant enrichment by adding a resistance in series with the coolant sensor to cause it to operate in the cold enrichment zone all the time. The primary temperature based fuel compensation correction occurs through the intake air temperature sensor.

On a 1971 B20E engine running all the correctly matched components for a 1971 D jet system, you would typically be running with an AFR somewhere in the 13s at idle. Your modest 5% capacity increase should not cause you to go really lean, particularly since you have cranked up the fuel pressure. I would check to make sure that you don't have mismatched components or that you have other fuel delivery problems. Be aware that on the 1971 and up D jets, there will be a adjustment potentiometer on the back of the D jet controller that is specifically for adjusting mixture at idle. If you are running the batch fire D jet system, your AFR needs to be in the low 14s to 13s to get a reasonable idle.

If you want to run the D jet system, I would not mix an match components. I would stick with all the matched parts for a 1971 D jet system as used on the B20E. Cranking up fuel pressure will increase fuel delivery. You could use it to make small tweaks; but, if you need big corrections then you are going to skew fuel delivery at idle or at WOT depending on which way the tweaks go.

It is unlikely that you will get fuel delivery exactly right using the D jet system. If you want to get fuel delivery closer to ideal I would switch to an aftermarket fuel injection system while retaining the D jet manifold and fuel delivery components.