Not the FE engine price so much but with an engine not intended for the car, items add up. These are a few of them.
For my 1948 Lincoln Headers wouldn't fit but CI shorty's do.
Oil filter adapter- had to get a 1976 4X4 no others would clear the steering box
Car oil pan hit the cross steering rod. Had to change to a 4X4 rear sump pan
Had to recess the steering box into the box frame
New wiring kit since the old cloth wires were modified so many times the electrical tape was a ball of plastic from engine heat. The prior engine was a 1957 Caddy.
Tri power air cleaner required a lot of surgery to the firewall.
Shaving doglegs out of the frame for exhaust header clearance.
These were all surprises above the fact that I knew I'd have to build engine and trans mounts.
I did find that the 4 bar and 9" rear axle conversion wasn't that hard. The 48 Lincoln Continental however is a unibody car so all cutting & welding was under the car so fire was a concern.
The engine rebuild at lease is on a stand with adequate room.