I would go lower - low 40's. The Non-original engine hurts as stated above.
What is the original paint color (interior/exterior).
How is the dash?
Mileage on chassis?
Provenance (where has it lived)?
Yeah - more information and then we can help with a firmer price.
Start higher than you think and be willing to go lower. A non 'matching' car is not a bad thing, but it will not fetch the $'s that you think.
Then again, all you need is 'One'
