Clayton, just trying to learn something here - what gives it away as a lash-up? The wiring looks sloppy and the serial plate is crooked. Anything else?
The serial tag is obvious. The parenthesis are the first giveaway, the aluminum material is the second. I had started a large thread over on the old plexi palace forum regarding the MG/Harrison fake-watt amps. I don't know if the photo hosting site that I had many of the pics on is still operational. Look at the parenthesis on this particular tag. they are not the right size, they are tool large. This is the biggest giveaway, an instant red flag. Never buy an old Hiwatt with these parenthesis unless it is just a couple hundred dollars.
The transformer date codes are from 1976, making the original amp either a 1976 or early 1977.
An all original 1973 would not have had holes for and IEC mains plug underneath a bulging plug.
it has the mid-late 1970's preamp, not what would be found in a 1973.
The fuse holders in it are consistent with a 1976-1977, not a 1973.
Thanks, I remember seeing that thread and am aware of MG's practices. I emailed them years ago about an amp they had on gBase and they never responded. Probably lucky for me!
I thought they were in some serious legal trouble recently and they stopped production of Hiwatt but I saw a recent ad for them in a magazine. Hopefully somebody more respectable has it now.