Bit of an update:
In deciding what spec I should go with, I have spent a lot of time thinking, doing internet research and asking opinions and listening to answers. This included PM'ing some members on here who have relevant experiences with the type of questions I was asking - Thanks to all who shared their thoughts.
I have been fairly conflicted on the subject, and still have a little doubt, but
the spec I have decided on, is to keep it a 3.4.
Keep a dual mass flywheel rather than go single mass light weight, but pretty much upgrade and strengthen all that can be done.
I know that some of you are convinced a 3.7 is the way to go, and ultimately of course, given more money, that was on the table.
My decision is partly financially driven, though the increased cost of the 3.7 wasn't too far out of the ball park. Ultimately though, cost was not the final arbiter.
I have been happy with the performance of the 3.4. Sure there are faster cars, but I like the combination of a revy engine, and enjoy the process of allowing the engine to "rev out" to the redline. Having to change gear to get the oomph is not an issue for me. Admittedly, I haven't had an opportunity to drive the bigger motor, but I think I'll be happy enough with an "optimised" 3.4.
A 3.7 would be a more flexible, grunty motor. Plus allow scope for future upgrades to camshafts induction and exhausts, and ultimately give much more torque and power.
However, I don't want to get into all that. Its expensive, and I feel I have "done" that with my last car which I rebuilt with forged high compression pistons, flowed the cylinderhead, bigger valves, made a bespoke tuned length stainless exhaust system, fitted bike carbs on a bespoke designed inlet manifold etc etc etc. Great fun, but a lot of money, and other cars were still waaaay faster (and cheaper).
OK, Single mass flywheel. This was a difficult one. On the one hand, having handled the Dual Mass Flywheel together with the clutch, let me tell you its a
massive piece of pig iron hanging off the end of the crank!
Also, after speaking to a few specialist Porsche independents and owners that have fitted them, there appears to be little evidence from them as far as crankshaft failures go. The only constantly mentioned issue is "chatter" at idle or very low rpm.
But despite this, there are many well sourced and referenced "experts" inc. Porsche themselves, that say that harmonics, combined with upstream stress loading from the drivetrain, can destroy the (sintered not forged) crank, not to mention the extra vibration and stress caused to associated parts such as gearbox internals, camtrain etc. In the end, I had to make a decision, and being that I am into future proofing the engine so that it lasts at least another 10+ years of no nonsense mix of driving conditions including commuting, touring and a fair wack of Sunday morning B road thrash, I have decided that, for me, I will trade the potential gain in low gear engine response for peace of mind. Also, this is my only toy, I don't have access to lots of high end motors. unless you include my Ford Puma 1.7
For me in this case, less is more as they say....
There will be opinions on that I'm sure. Would engine bearings last longer with a lighter flywheel for example? I don't know, but they generally last between a representative, (based on received wisdom) 80,000 to 120,000 at the moment (Plus lots of cars that do much more).
So in essence the spec is:
6 x new cylinders
Large IMS bearing in re-engineered intermediate shaft
New chains plus tensioners and pads
2x cylinderhead overhaul inc valve stem seals.
New bearings (Of course)
ARP conrod bolts.
I'd also like to say again, just how patient and generous with their time that Hartech have been. You might consider that to be taken for granted, but I for one don't. When you have spent time phoning around to get a base to reference something like this on, it quickly becomes apparent who actually seems to know what they are talking about. It is surprising just how many companies say "Oh we don't release the details of who we use for machining" or where they source the parts from, or whose pistons they use etc. Just expecting the customer to accept that they "know best".
Time wise, I'm looking at somewhere between 2 and 4 weeks before I have the thing back, so maybe by the end of May it'll be back in the car and I can start running her in. Can't wait!
Cheers