I agree with rolla 16v that there are some suspicious marks on the front rail near the inboard engine mounting point. You should look closely at the underside of the rail to see if it has been broken, then welded up to repair it. If that has happened the frame alignment could be in doubt. The engine-side clutch half has set screws rather than a captive cotter, which may mean that it has been replaced. Failure of the original captive cotter clutch half seems to be a common cause of cracking or fracturing the front rail, so it may be that the machine's history is starting to unfold before our eyes. Coupled with the replacement engine and catcher, and whatever doubts there are about the possible alignment problems in what may be a broken-and-repaired frame, this does not strike me as a very original or high-quality SB45.
At $550, if the chains and sprockets turn out to be new, and the engine was bought new as well, adding in the approximately $200 the aftermarket catcher would have cost, the price is in line with the cost of materials to carry out the refurbishment. However it is very important that the frame alignment is correct after the welding repair that seems to have been carried out. The reel looks to have a reasonable amount of life left in it, though it seems to have had at least one heavy resharpening operation, and I can't see the bedknife to see what condition it is in.
