Hi Joe,
If you were planing to customize as per your image above then I'd opt F5 Cobra, and if sh!t happened, then I'd look to sell the engine and roller separately.
It would cost you less up front, you are familiar with the F5 product, and you sound like you'll be happy & competent to do the labor yourself.
There would be a market for both a used Cammer and a used F5 Roller & I suspect you'd lose less on the turnaround.
If you did the above to a Kirkham... I fear you may limit the market that would purchase it should things take a turn for the worse.
Either way, Its your call and either car I'm sure will provide you with ample enjoyment and indulgence. Your only concern should be that you don't make this a case of paralysis by analysis - Kirkham vs F5 - and it takes you a further 10 years of research before you make a play.
Best of luck with your project, it sounds like it will be a helluva toy...
