older cowl prop extension 21/4 or 4 ?

My kit has the old white gel coated cowl of early 90's vintage.(I know chuck it and order a new one) I've been reading about how Vans modified the cowls to all accept the 21/4 in extension from the earlier 4 in. Is there anyway of telling which version I have or does it matter. Can you just trim the older style to fit the shorter extension? I've emailed Oregon but haven't heard anything back.
Hoping to hang the engine next week.....
Thanks
Skip

egp8111 said:

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Can you just trim the older style to fit the shorter extension?
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Hoping to hang the engine next week.....
Thanks
Skip

Click to expand...

No, I tried this and lost a few months...

The old white extended cowl is too narrow for the forward O-360 cylinders if it's trimmed back.

The new epoxy cowl is so much stiffer than the floppy white one that fitting it is much easier.

Buy the new one, well worth it...

ADDED, the above if for a RV-6, but I think the RV-4 may be even worse due to the side cheeks.