That is the joy of the watercooled T25, engine upgrade possibilities are endless.
Non-turbo diesels tend to go for less as they aren't so desirable, as it's already got a golf diesel engine fitted a gti upgrade is meant to be fairly simple. Or you've allways got the 2.1 injection watercooled (112bhp) which was a standard model later on. An Mi16 powered T25 would be pretty awesome. Seen quite a few running MK3 golf gti engines and a couple with porsche engines running nitrous!!!