Generally speaking, the earlier the silverface model is, the easier it will be to blackface. The most difficult ones to BF are the late 70's 135w ultra-linear models.
Most of the differences are in the phase inverter, if I recall correctly(been a long time since I have done it). Most of the parts can be found at basic electronic suppliers like Mouser electronics.
You will have to find a schematic for your model, and one for a mid-60s twin, ...just compare the differences.
I would go for it...easily blackfaced, altough the early 70s twin sounds good regardless. Get a cap job, and maybe a set of tubes with a proper bias. You could sell it and get your money back at any time, these amps will only go up in value