Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
I think before I invest in another engine of unknown condition I would strip down your existing engine first to determine the condition of it and to determine what is salvageable and go from there. If you buy another engine it will be at least 30+ years old, countless owners, probably no history and you could slot it into your frame and get the same results.To be realistic, there are probably a couple of months decent weather left to go riding, it will take you that long to find a donor bike/engine and slot it into your frame. You would be better off stripping your engine down before the weather gets bad, seeing what you need (the cost will go on rising!) and start gathering the bits together for a rebuild. As Bryan has said the bits are out there to rebuild these engines and what else are you going to do over the winter whilst the O/H is watching Strictly on the TV? You could spend it in a cold garage getting to know the innards of your motor and come spring it will be rebuilt and you'll be proud of what you have achieved .The best thing about this forum is the number of experts on here, advice is free and willingly given, all we ask for is plenty of photos (we like photos over the winter months to keep us all going ) and the occassional donation to keep this great forum alive and kicking.Good luck with whatever you decide to do.