G'day mate, if you decide to go with a new box rather than second hand, we have them all in stock - just thought I'd mention them since some people may not know we stock gearboxes:
Type I IRS (4.12 R&P):
http://dasrestoparts.com.au/rancho-transaxles-early-irs-gearbox-1969-1970-type-i-no-core-exchange-required.html
Type I IRS (3.88 R&P):
http://dasrestoparts.com.au/rancho-transaxles-type-i-irs-gearbox-1973-3-88-ring-and-pinion-no-core-exchange-required.html
Type I IRS Pro Street (4.12 R&P):
http://dasrestoparts.com.au/rancho-transaxles-pro-street-irs-gearbox-type-i.html
Type I IRS Pro Street (3.88 R&P):
http://dasrestoparts.com.au/rancho-transaxles-pro-street-irs-gearbox-type-i-with-3-88-ring-and-pinion-no-core-exchange-required.html
Cheers
Al
DAS RESTO PARTS
07 5568 0143 (Gold Coast)
PS As per the second hand beetle gearboxes out of beetles, they will have a type I nosecone (as do the boxes we have in stock) so you need to factor in a type 2 nose cone and possibly hockey stick to fit into your splitty.