That S-10 frame swap to the '51 is going to be a challenge unless tou are an experienced builder and modifier. Your biggest problem is going to be in the area of the steering box. The S-10 steering box is so far forward of the frame it's going to interfer with the inner fender, radiator support, and grille. A lot of modifications will make it work, but you'll be swearing all the way. An alternate plan would be to do a subframe graft to your original '51 frame using a '67-'69 Camaro or '69-'74 Nova. They both have the steering box mount at the rear of the front wheels. I've used this set up on a '54 and'49. Now the easiest solution of all is to contact Chassis Engineering or TCI and get one of their Mustang II rack and pinion front cross members that are made for your '51. They work real nice but they are expensive. Good Luck.
