I don't have any connection with this firm, but you might want to check out their software package for Form 709.
https://www.puritas-springs.com/product-category/federal
If you wouldn't consider preparing your 1040 manually (without using income tax preparation software, such as TurboTax), then you should most likely not consider preparing a 709 manually.
As a footnote, prior (taxable) gifting (i.e., above the annual exclusion) only serves to add more complexity to the equation.
