Apparently, parabolic don't affect the VIN; they are regarded as an in service replacement of wearable parts. The suspension points for the VIN exclude wearing parts such as springs, dampers and bushes. That is pretty much all we have for suspension, with no rods, arms, struts and such, but those are the rules. So, you should have enough points not to be a problem. Swapping the rear axle will have cost you both points for axles, though.
I contacted the DVLA a few days ago about the whole points thing, because I'd like to do something similar to your transmission mod, and wasn't sure about my interpretation of their registration guide ( https://www.gov.uk/vehicle-registration ). It would be tested for IVA under a radically altered vehicle or an amateur built vehicle scheme. The former is for professional rebuilds and includes several very costly tests. The latter is advantageous to us as there are no tests other than the basic inspection, but we have to be able to show that we built the vehicles ourselves and for our own use. This is in the response from the inspector. More of concern is the comment that the IVA is performed and then they decide on the points awarded (seems logical), but the wording in the guide and the letter I got strongly suggest IVA is mandatory for all modified vehicles, regardless of whether we have worked out we keep the 8 points required. I'm awaiting confirmation of that. It might be a rule change, or it might be a clarification of an oft misunderstood rule - I don't know.
Your spec is much like mine, except I have gone PAS, so lost the steering points. You have more wiggle room with the original steering, so should still qualify for the original VIN. It's not the end of the world registering from new, but it is a shame for those with tax exemption to lose that (you would if under 8 points). I didn't get a clarification about road tax band and the registration date, but literal interpretation suggests that we'd be paying on emissions bands on a new registration, which looks like it could be very punitive with a Tdi. I hope that is not how it works.
As for the LT77 and LT230, it'll be a stronger, quieter and less leaky combination than the standard transmission, and it can be fitted without major chassis alteration. Those who have fitted it are all very pleased with it. Brackets and mountings are not considered major chassis structures and the DVLA aren't concerned about them. It's wheel base length and cross member removal that loses the VIN.