ILR documents query

Hi all,

I will be appying ILR in march this year and unsure of what the kind of documents to be sent to Home office. I will be applying in combination of work permit and Tier 2 general.
From all the five year, i have NOT got the P60 forms for the first 2 years(2005 and 2006) which i requested to my employer. They have send me all the tax/salary records on company headed paper for the financial year 2006/2007 but they are unable to send me the records for financial year 2005/2006 due to changes in their payroll department.
here goes my queries:

1) Are these kind of documents on company letter head are acceptable to Home office as prrof of employment/tax ??
2)If they are unable to give me the tax records for that financial year 2005/2006 what other documents i can show as proof ??

3) i have got original Home office work permit letter (accept one extension). Can these be used as evidence to prove ??

4) i have got form P45 from the same employer which shows my tax details through out the period i guess.. So can these be alternative documental evidences ??
Please see that i received salary slip from them but have lost few of them so those evidences are ruled out.

Any help/suggestion will be appreciated.
Suggestion with the link to home office website to confirm as a proof will be even better.

Thanks in Advance..

Cheers,
Deep..