Please give me your thoughts in a spontaneous reply, would you go for it despite it not being an urgent must at the moment.
They are a very nice cylinder head but lacked quality control (pride) if my one is anything to go by which was disappointing given the low number made.
If the head you are looking at is anywhere around #170 you need to check the ports for signs of a die grinder being used in the bowl to insert transition which means you need to check the valve seat faces very carefully for damage from the same tool.
Here is your predicament.
At this point in time there is no production of these heads (as far as I know) but manufacture of them will start again ? in the USA via the new manufacturer at some point.
We would hope that person will not only turn out a as new product (without swarf still stuck between the fins ) but also address some of the other oddities like the retained weak 3/8-20 tpi threads.
The future cost is unknown, will it be more than the head you have been offered or less.
Would I buy another one, no unless I was only looking for something that looks pretty from the outside casting wise based on my bike coming stock with an RH10 that was in fine form.
The irony for me is I only bought the FA head to avoid sending the RH10 out to have the seats done because there were few places competent (but found SERCO Motorsport since then)
The 850 FA head cost close to $4000 with valve train components , the 750 RH1 head JC did for me cost $1300 and that includes buying it off US eBay, having it posted to Jim and to have the seats done, guides installed, Kibblewhite valves supplied along with alu/bronze inserts on the exhaust ports and three 3/8 studs and post to Australia.
In hindsight I could have sent the RH10 to him for a fraction of the cost of the FA even with double international post, the bonus being you actually get a head ready to bolt one but no fancy box with contoured polystyrene packing to put on the mantle piece.
If you have a cracked RH4 that might be something else but I would wait for the US version, why not contact them to see where production is at ?
If the FA head you are being offered is cheap it might be worth the gamble after close inspection just remember they were expensive but that is an expense you might get fifty cents on the dollar back on.
Just remember the FA head will not work properly unless you also fit 2.5 inch wheel rims and Avon tyres.