See
http://fsims.faa.gov/PICDetail.aspx?docId=8900.1,Vol.5,Ch5,Sec2 for how it's supposed to work.
Note - "
... Part-Time Practical Experience. During the evaluation of part-time practical aviation maintenance experience, the applicant must document an equivalent of 18 months for each rating individually, or 30 months of experience for both ratings. This is based on a standard work-week that has 8 hours per day for 5 days per week, or a 40 hour work-week, or a total of approximately 160 hours per month. The time is cumulative, but the days, weeks, and months are not required to be consecutive. The practical experience must be documented...." If you say 40 hours / week for 36 months (three years) you could say 40x52x3=6240 or you could say 40x4x12x3=5760. Or, even other calculations at the discretion of the FSDO.
The better the people at the FSDO know you, the better will be your reception when you approach them to discuss your experience. If you're a complete unknown, expect skepticism. Frankly, I think I'd feel the same way.
Work on experimental aircraft can count, but may not. It's solely up to the particular inspector. This will probably not be a "check the box" and "walk in / walk out" experience; rather, it will take some time and persistence. When they tell you "NO", don't get upset or give up. Just ask what exactly would be required to get to yes and stay with it.
I'd begin by reference to FAR 65.77 and the link above to the section of 8900 that describes the process. I'd also look at FAR 147 Appendicies A - D and be sure that you not only have the time requirement but also the topical coverage. (8900 requires experience with 50 percent of the material in FAR 147 Appendicies B - D.)
Lastly, it will certainly help, and may be a requirement, to have a recommendation letter (or letters) from a certificated mechanic(s). Internet searches can produce several good examples. So, plan on not only working with the FSDO, but with well respected mechanics as well.
That's just one perspective - I hope it's helpful.
Dan