Hi Chris, the Model 45 was first released in 1968, yours is much later than that....this I can tell from the following details....the solid/twin rail engine deck refers to the chassis design...the early Scotties had a solid panel of steel running between the side frames that the engine sat on like this one...
[Linked Image]
Yours has 2 steel rails between the side frames. wink
Another difference of the early machines is the screw fittings for the grass deflector, early: screws...later black plastic knobs, like yours.

Still another is the end caps of the front roller; early: alloy (see the pic above)...later (same as yours) black plastic

But the real clincher is the chain case attachment screws...early horizontal....later: vertical (Like yours).
See the earlier pic of the Scotty in this thread.
Yours is a late model machine, in my opinion. wink
Hoping this helps...
cheers2

Please do not PM me asking for support. Please post your questions in the appropriate forums, as the replies it may receive may help all members, not just the individual member.
Kindest Regards, Darryl grin