Re: interchangeable force powerheads
Basically a qualified no, with this proviso: The 1999 powerhead has different splines in the drive shaft/crankshaft than the 1990. IF, however, you can mate the upper driveshaft of the 1999 to your 1990 lower unit, (it should be a 2 piece drive shaft and the splined coupler MAY be the same) then the powerheads are all the same bolt pattern and can interchange.
You may also need to change some associated hardware like the mounts for control cables, shift linkage, and possibly the timing tower shaft. The basic block is unchanged since West Bend/Chrysler made them.
The only real problem is the crankshaft splines.
