Man, that's a tough one Mark. He has the POP which confirms the L78 originally, but I assume no formal paperwork confirming the L88 warranty transplant, just the word of the original owner.
To be honest I can't really qualify myself as an expert in placing value on a 68 L78 El Camino. You would need to deduct a certain percentage for lack of original engine, then add a certain amount for the L88 which is definitely worth some bucks.
Final assumption - approximately 10-20% lower than a comparible L78 Elky with the original engine and in similar condition. Don't know if this helps or not
Good luck with it, sounds like a great ride
