All SEPs are a variation on a theme and its more a case of finding out the differences which you can usually count on one hand.
I would question anyone expecting more than an hour to convert from a PA28 to a C150 as being more interested in your wallet
Not uniquely, I have a big book of kneeboard cards I've produced for my own use, which remind me of the key values and features of whatever I happen to be flying next. That said, each one probably took me half a day with the manuals to produce.
Which is an important point I think. There's far too much of a culture in the UK of "just get in and fly it". There is a reason why we have POHs and similar documents - it's to learn about the aeroplane before you get in it. The pilot who takes their time with the books to get to know the aeroplane, probably will do it inside an hour.
The pilot who doesn't will take more hours, and the instructor who doesn't ask pilots to spend some book time before flying, is probably just after the hours.
G