Congratulations on your find. Like buying any car check it out thoroughly.
I have a Butler #42 and I love the way that is is engineered. During my build I have added my touch to enhance it further. You will find the serial number and date of manufacture stamped on the frame on the left side at the very front of the frame by the vertical bracket where the body is bolted to the frame.
You can see some of my build photos here in my albums on this Forum or on Facebook where I have an album that is more up to date.
The engine bay should have two aluminum heat shields between the headers and footwell. You can always add more insulation if heat is an issue. I have blowers in each footwell.
Front suspension. If it needs rebuilding you should seriously consider looking at the front suspension made by FastCars in Michigan. I totaled the cost on what I spent to rebuild my MGB front suspension and the cost of the FastCars IFS was not that much more. So I pulled out the MGB IFS and got rid of it and now have an IFS that is worthy of the car.
There are three of us on this Forum that have FastCars IFS suspensions. Forum User Names: SoTxButler, Russ in Texas. Donunder, Don in Australia + one other guy in Europe. Russ & Don would be happy to comment. Don has the Arntz a pre Butler car.
Russ is also keeping a record of all Butler cars/owners. So if you buy it, let Russ know as we would all like to know where the 103 +- Butlers are. Ron Butler who built these components lives in California. He is retired and still has some components/spare parts in inventory.
Rear suspension is Jaguar XKE/XJ6/XJ12/XJS and is a great suspension. If you ever rebuild you may want to get rid of the needle bearings and needle thrust bearings. There are a number of companies that create rebushing kits using modern
synthetic materials.
The butler frame is STRONG. And can handle a lot of power.
Depending on how you plan to drive the car you may want anti-sway bars on the front and the back if not already fitted. If the front has one the FastCars IFS should mate with it should you make this upgrade.
Good luck and I look forward to hearing back when you are the new owner.
Arthur