The SRG 1125 is a one-size-fits-none form
Do the best you can with it (it didn't cover me either - mil heli IR). Even better go down in person and get it all done in less than an hour. then you don't even need the payment form as you can hand over your debit card.
The key bit I think in your case is:
An applicant who holds an ICAO IR(A) or military green Instrument Rating (Aeroplanes) and has passed a single-pilot IR test in the 24 months preceding the date of application for the IMC Rating will be credited with a pass in the initial IMC Flight Test and the written examination. The applicant must apply for the issue of the IMC rating within 24 months of the last IR test passed, The IMC rating will be valid for 25 months from the date the last IR test was passed.
The initial flight test and ground examination Omit Sections 6, 7 and 9
You practically don't have to write anything!