A Form 1 and a Form 4 are different forms.
I have used a revokable living trust - much cheaper, easier and no public disclosures to file... and no annual fees or meetings necessary. From what I understand the requirements for a corporation and trust are the same with regards to paperwork. If a dealer currently holds the MAC, they should be able to help you with the Form 4.
From my experience with trusts (which should be extremely similar to corporations), you'll need to submit:
1. The NFA forms in duplicate (Form 1s or Form4s, there is only one valid version of each)
2. Form 5330.20 in duplicate (Certification of Compliance/Citizenship)
3. A copy of your declaration of trust - or in the case of a corporation, the notarized Article of Incorporation (You might also need to send in your state's certification that the corporation is a legal entity, registered with the state)
4. A check in the amount of $200 for the machinegun or $200 for the SBS
When you sign the Forms and the Certification you need to sign and ALSO identify your title (e.g. for a trust you'd typically be the Grantor and Trusee - or in the case of a corporation, I'm guessing the President). With regards to HOW you fill out the forms, it will be the same (type) information for both a trust and corporation. For a few pictorals of the trust route, the following website has some good images. They will get your started in the right direction.
Arizona Gun List