https://www.performanceparts.ford.com/part/M-4204-F28A
9" TRAC-LOK LIMITED SLIP DIFFERENTIAL| Part Details for M-4204-F28A | Ford Performance Parts
9" TRAC-LOK LIMITED SLIP DIFFERENTIAL|Ford Performance Parts
https://www.gov.uk/aaib-reports/enstrom-f28a-g-bhvs-15-october-1982
Enstrom F28A, G-BHVS, 15 October 1982 - GOV.UK
enstromgoctoberuk