I did it, with trepidation, on my last build but used new lifters and followed normal flat tappet break in procedures.

To support what has been said. Sonic test is handy to check core shift and see if a block is a candidate, but as has been said it is purely a spot check. Below is the sonic I did at home on my current engine before I punched it out 040 (had pistons). Whilst not fantastic it looked to acceptable. When bored, porosity was encountered in one cylinder and a sleeve was necessary.

They will have cost saving targets tied to bonuses. So will do what it takes to save a cent or two on a part or process, real or not. I used to see it often when I worked for a tier 1 automotive supplier. An engineer would say we can save 5c a part by outsourcing......a couple of years later a new engineer would come along and say we can save 5c a part by insourcing. All bullshit on paper of course but so the merry go round begins. My own target was a $1 million per year. I used to think that if all these savings across the business were real then we would be making parts for zero cost in a couple of years!

Can anyone please confirm the OD of the front leaf spring bush? When I put this car together I cant remember if I used the original leaves or Australian ones. Measuring the bush OD on the car is difficult but from what I can do, the measurements are not filling me with confidence that the Australian ones will fit. Looking for some degree of confidence before I pull them out. Thanks.

I looked it up in the NHRA rule book for stock eliminator and it reads the stock mounting points must remain. It looks like they wouldn’t be legal.

But do they have to be used?

I have tried many electric fan combinations over the years and they have always resulted in overheating. I think they need to be carefully matched (or fluked) to radiator fin/tube density. Nothing has come close to the big factory paddle fan and shroud.

Why is it that a Bosch O2 sensor will last 100k-200k miles, and probably 15+ years, in a new vehicle, but seems to fail fairly quickly in any aftermarket setup? And these cars are typically not being driven in snow and rain. It seems odd to me.

I would think it has to do with the power up protocol. I used to use an Innovate LM-1 and never lost a sensor. Used to start engine then immediately power up to avoid thermal shock.
Lost my first Sensor on my Holley Sniper a couple of months ago. I think that was thermal shock. I gave it two primes on a particularly cold day so the sensor would have been close to fully heated before I hit the key. That one lasted 8 years. I suspect the OEM's have better control on the heat/start protocol. I also suspect the OE tables are so well dialled in that unless it threw an engine light you probably wouldn't even know if you shat one.

We have them here in europa Opel Record with 4 cyl or Comodore with 6cyl

Don't think they are quite the same car Heo. Similar though for sure.