a couple of questions
is the 67 and the 68 are about the same
about how much does it cost for a 351 with twin turbos
can i fit anything bigger than a 351. or is it too big
and should i keep the the r-3 gears or put the m/t r-4or5
#2. A few people have put 460's in them. And you can build a 460 even larger C.I. than that. So, you are not limited to a 351.
#3. If you are asking about 3 speed, 4 speed, or 5 speed, that would be your preference. All can be put in. Standard or Auto.
To put in a 460.. it will be tight.. but fits.. use early 429 70 mustang small tubes and make it happen!! It is better to get ahold of Crites and he has templates for notching the shock towers to aid in spark plug removal..LOL