Anyone have any insight on how a transaction as follows would likely work from the dealer view?
I want to trade my 2000 Boxster S with 54k on it (#113 which sometimes matters) and 2004 Saab Linear with 125k on it. I pay difference in cash. The Boxster is in excellent condition, drives like a new car. Bilstein sports and H&R's all around, B&M short shift, Beluga Exhaust (all last 5k miles). Stuff a dealer doesn't care about but the right buyer would. The Saab is a dependable car but getting up in mileage. Just did exhaust, radiator and thermostat a couple thousand miles ago. Runs great. Does the dealer just look at the trade in value and offer me that for the two cars or does he say I can likely get this for these cars and go from that? Hopefully that makes sense. Based on what little I know, I could get likely 13-16 for these. An issue i think is I did most of the preventative stuff on the Box within the last 4k miles (IMS, water pump, brake fluid) which I don't think a deal even cares about.
I would love to sell my stuff and then buy but that takes time which not sure I will have with this car. It's that pretty.

Any insight?