heres 2 cents from someone that is in the same predicament as you. I want a 08+ diesel screw SOOOOO bad. but I have a 72 c-10 w/ a 454 that I need to restore, so i opted to keep my good lookin f150, and build the **** outta my BB and c-10. trust me, you'll have more fun in the muscle car then you would in the diesel. 1 day in the muscle car will trump a whole YEAR in the diesel....
i would go with the muscle car, its more unique and would be more fun! plus you wouldnt have a huge payment every month you get to look back and say that YOU actually built or restored the car.