Convert Large Excel VBA Application to Python (Excel Front-End Retained) — Experienced Migration Specialist -- 2

We are converting a mature, commercially deployed Excel-based financial/audit automation application from VBA to Python. The Excel workbook front-end and custom ribbon stay; all processing logic moves to a Python engine running behind Excel.
THE SYSTEM:
• ~56,000 lines of VBA across a main workbook and add-ins, developed
• Modules include: data import and mapping wizards, journal/adjustment engines, configurable settings panels, analytical calculations, multi-step report generation wizards, sampling tools, and a cash flow statement engine
• Full installed environment, source code, and user documentation will be provided under NDA
SCOPE OF WORK:
1. PLANNING PHASE: Analyze the VBA codebase and produce a technical planning document — module inventory, proposed Python architecture, data structures, QA approach, and time budget. Three client-provided test data sets will be supplied as the QA benchmark.
2. DEVELOPMENT: Clean re-architecture (not line-by-line transliteration). Legacy resource-file dependencies replaced with JSON/config structures. Report boilerplate externalized to editable template files. Modular, documented, deduplicated code.
3. PARITY TESTING & UAT SUPPORT: Python outputs must match the existing VBA outputs on the agreed test data sets. Defect fixes during the client UAT window on a fast turnaround (blockers within 2 business days).
REQUIRED SKILLS:
• Proven experience reading and reverse-engineering large legacy VBA codebases
• Strong Python, with specific experience integrating Python behind an Excel front-end (xlwings, COM add-in, or equivalent — tell us your preferred approach and why)
• Disciplined output-parity testing methodology
• Clean written English for technical documentation
• Accounting/audit domain familiarity is a plus, not mandatory
TIMELINE: Planning document within ~2 weeks of start; development approximately 8 weeks; then UAT support. Total engagement roughly 3 months.
PAYMENT: Fixed price, milestone-based — (1) planning document approved, (2) build delivered, (3) client acceptance complete. Payment released per milestone through this platform.
TO APPLY, ANSWER THESE THREE QUESTIONS (applications without answers will not be considered):
1. Describe the largest VBA-to-Python (or similar legacy) migration you have personally delivered — size, approach, outcome.
2. How would you architect Python running behind a retained Excel front-end with a custom ribbon? Name your stack and its trade-offs.
3. How do you prove functional parity between old and new systems when the business logic is undocumented?
Start date: within 1 week. Long-term follow-on work (AI-assisted features, Phase 2 enhancements) is likely for the right person.