I'm surprised to hear that the 65 sportster is a light engine. I have a 45 sportster and it's a fair bit heavier than my 46FX... I'm saving it for something that needs a lot of nose weight like a slow poke...

As for the trainer, due to the weight and size issues of the 65, I'd ****etaboutit... either get yourself a decent new 46-52 or pick up a decent used one to keep the trainer going...

As for the 65, run it up on a test stand and take the time to break it in properly. You might find it'll be a good match for something like a 4*60 or Tiger 60.....

Addition: I've got a 65LA that was in my first trainer (Superstar 60). After burying it with the aid of a Hobbistar.. it's been laying around for a while. Now I've discovered that it still runs nicely and turns an APC 13x6 @ over 11,000rpm it's going in my Tiger...