A lot to mention here. First of all, when you order a FP manifold, you need to know whether you need the manifold to have holes sized for 8mm bolts or sized for 10mm bolts. The 650 (6m6) and 701 (61X) cylinder use 8mm bolts. The 62T 701 cylinder uses 10mm bolts. FP sells manifolds for both.
If you already have a manifold with 10mm holes you can use it on your 61X or 650 cylinder, but your best bet is to assemble it with the head off so that you can position it properly relative to the exhaust outlet (since there will be play with 8mm bolts in 10mm holes). You can also carefully drill out 8mm holes to fit a 62T 10mm application.
To add to this, if you are buying used, you may end up with a manifold and/or headpipe with a very small diameter exhaust hole (I believe the early ones were 42mm as they took the B pipe design right from the Kawi, in fact the Kawi and Yamaha headpipes are interchangeable, or were for many years). As you go to 760 and larer motors this can restrict performance. Now FP sells the 701 setup with a 47mm hole so you are pretty good for most applications until you get into the 900+cc range and then you can have a builder carefully open it up further (this is very close to water passsages so you really have to be careful).
Hope this helps.
