302 to 400 engine swap??
 

is it posible to swap a 400 ltd motor in my 77 f-150 2wd 302 truck? how much work would it take? could i use my same transmission out of the 302? or should i just rebuild the 302?

You could do it, You'll need Frame mounts. The tranny behind your 302 won't work the 400 uses the Big block bolt pattern. If your wanting to up size your motor the 351w will be a bolt in swap.

Your tranny will not mate up. A 300-6 would also mate with your tranny. The 300-6 has more torque for a truck application.

A 400 from a truck would be a better choice than a car because the brackets would be for a truck.

If you have a 302 in the truck now you can use the same frame mounts for the 400, but you won't be able to use the mercs mounts, you'll have to buy them for your year truck application.
Can you use the trans from the merc? the one behind your 302 will not bolt up.