The older ST .90 made in Italy had a removable front housing. Larger ST's also had a removable front housings. I think the sizes were 2000, 2200,2500 and 3200. Also Moki has a removable front housing.

Measured intake timing on ST .90 (standard rotation):
Intake opens: 135 degrees BTC
Intake closes: 50 degrees ATDC

With rotated housing and reverse rotation the timing will be:
Intake opens: 140 degrees BTC
Intake closes: 45 degrees ATDC

Intake timing indicates the engine should run successfully in reverse.

Measured weight ST .90 with torpedo muffler = 25.3 oz.

A 12 inch diameter prop might be somewhat small.

Bill